Sorry if I repeat something, as i had no time to read trough all the topic, last days, but I wanted to give my two cents. I'll make a difference if looking to Civ VII or keeping in Civ VI, as for Civ VII the idea is quite "revolutionary" - just remove half of the victories (well, not remove, but merge). For Civ VI, one of my main desires is, if they do a new pass, they focus in victories, so I'll look for arrangements in the ones I think are quite boring/unbalanced.
So, if we are looking at CIV VII:
Just keep two victories: Miliary Domination, and Cultural Domination (or, which is the same, "warmonger" and "peaceful" victories). In original Civ games (Civ I, Civ II), you had Scientific and Military, and Scientific was there because it was the "peaceful" way to win the game. Then, additional victories (cultural, diplomatic,...) were added when more mechanics were added to the game, but indeed, what we are looking there are different ways to make your civ win without wiping out the opposition. As more victories are added, it is inevitable some of the old ones (scientific), or some of the quickly implemented ones (diplo in civ VI, clultural in Civ V vanilla feel just bland), while - actually - they are part of the same thing: making your civ win by outgrowing, and not conquering, opposition.
So, what is the proposal? As cultural victory is, since Civ V BNW, the most evolved version of the peaceful victories, keep it, and make all other non-war victories contribute to it: religious dominance? >> increased cultural pressure (it already is!); space race (/scientific) achievement >> tourism (
or "fame"*) boosts; economic dominance (if you add it) >> increased cultural pressure (as already implemented in monopolies & corporations, but with a sensible formula), diplomatic victories >> tourism boosts (indeed, if you like more the diplomatic victory, you could keep the "leader of the world" layer, with tourism
/fame* being an important factors in how many votes you get for this position.
Note that I'm renaming "tourism" to "fame", as I think it is one of the things Humankind got right - naming which is the factor that will make your civ win peacefully: it is not bermuda-wearing shrimp-skinned people, but actually people in other civs that care more about yours than theirs
Ok, now let's keep in CIV VI. Of course, dismantling the victories is not an option so, ¿what can be done otherwise?:
Score: that one is easy: balance the pace/lenght of the game. In civ V, score victory was quite common (at least for me), because you barely had time to push the other victories, specially the late peaceful ones (science, culture), so you might end with a Score victory. It felt like a "consolation price" result, but I think it was a great effect indeed. You won the non-specific victory, meaning you could have won another victory, but were not fast enough. Now, in Civ VI, probably due to yield creep, we have T<200 victories... and T<400 victories for the AI, over a 500 turn limit. It clearly shows either the turns should be lowered, the yields decreased, or the costs increased to balance it out (AI's should be normally wining, if any in the 450-500 turn range. And players should have it really hard to complete a game in less than half the turns).
Cultural: As commented above, probably the most fleshed out and the one requiring less change. Some things that could be used to improve (actually to enhance and increase the involvement during the game), could be),
- Additional "early" rock bands (poets, bards or troubadors in classical / middle ages; storytellers or teather companies in industrial-modern), which less of a tourism impact (as said for score victory above, whe do not want yield creep), but maybe with influence in other systems (espionage, loyalty, diplo favours).
- More and more artists and works of art (reduce yields, but make the theming game something everyone can play at).
- Theming for literature and music (in other threads I already specified the details, but summing it up: both amphiteater and broadcast station should be able to store writing and music, and some combinations of writing+music would theme).
- (edit) Also, as commented by other posters, increasing the involvement of airports in tourism victory is a must

Domination: Fine as it is. Some commented about population and land percentage, and I say I agree with the concept but I think, with the introduction of the loyalty system, this requieremet is more or less introduced as you probably will not be able to held capitols without conquering or razing surrounding cities (and razing feels OK for domination). It also makes the victory not drag to long once you have 1/2 of the world conquered.
I would balance, however, GDR's. They are helpful to make the victory not drag to long, but also not very funny (essentialy an all-purpose unit) and less funny if you are in the opposite end. Make several tipes of late game juggernauts with rock-paper-scissors relationsip and different achilles heels and it could work better. Domination "fun" is the unit interaction. Some examples of what can be added:
- maybe an EMP-pulse missile unit can disable GDRs and other units (and city attacks) for some turns, but have no other effects;
- quick and cheap hit and run swarm-type units can be implemented, dealing important damage to bigger units, and resistant to any type of movement block (zoc, the previously said EMP), but on the other hand, being glass canons destroyed in one hit.
- also hard-to-destroy hovering fortresses might be included, really resistant and hitting everything around, but doing reduced damage and slow to move. (This is, more targets per turn, but not being able to one-shot kill anything)
Religion: I find it OK. Altough I'd agree it is mainly apostle spam and thunderbolt fights, I don't find it is so bad in that sense. It has some strategy (how many apostle packs, which promotions...) altough I would agree it ends up being dull.
- A thing that could help is to differentiate and enhance other units (mainly gurus and inquisitors, so apostles are not the do-all unit). Give them their own promotion tree, even split some of the apostle promotions to them (you'll probably use inquisitors if they were the only ones to get the debater promotion, don't you
?). Make each unit class focused in one thing, and Add the option to re-charge (maybe with faith cost) so units don't become useless when all charges are use us, and then you would be able to allow a promotion tree on the religious units, making it a bit of more role-play.
- To integrate better with other systems, you could make some of these propotions "power-ups" for worship buildings, so religious unit mission would be not only spreading/defending the religion, but also increasing the benefits you get from them. (in example, a "prior" promotion Guru will passively double the yields of workship buildings in a 6-tile radius, or a "nunciature" promoted Apostle in foreign land will increase the yields you get from founder beliefs out of the cities of that civ).
Diplomatic (voted for rework): IMHO, it is curently too bland and to easy, and world congress mechanic is half-developed. Altough diplo favour mechanic is not at bad, I'll echo Civ V congress felt much better, mainly because you had control on what was proposed and discussed. I have already explained my view on how to rework it in other thread, so I'll just sum up here:
- Generate different "world congress offices" players can be voted for (maybe you can make it you even need to "appoint" your governors - I wont stop them from being used on the map, but it could be interesting you can't opt to an office if you don't have the appropriate governor - so, you won't be able to take the lead of the "blue helmets" without a promoted Victor, or the "UNESCO"-like office without Pingala...
- Player helding one office will have office-appropriate resolutions and control office-appropiate emergencies. Keeping on office will depend on proposed resolutions and emergencie's success.
- If emergencies/resolutions fail, another player can push a vote to get the office for himself. Participation on previous emergencies (points gained) /proposals (favour spent voting for or against) will help him getting the position.
- You would need to held a majority of the "UN" offices to call for a "world leader vote" on yourself. The more offices you have, the lower treshold you need to win the resolution (and the game).
Science (voted for rework): I'll say I even hate this victory more than diplomatic. I'll concede it is more fun to play for, but IMHO, it is horrible to play against (at least in huge maps, were you can't cover all the spaceports available). I think it needs more risk and ways to fight against it. Just building X projects does not work for me.
- Earlier, I considered a "spaceship control" mini-game, were you had to direct your spaceship to avoid black holes and gravitational fields (via the late laser shoots) in order to reach a safe destination (you could also try to re-direct and hamper the progress of an adversary spaceship). However, that would be maybe too gamey and isolated from the main game.
- Lately, I have tought of making you fight for the orbital control of the earth, in order to ensure your "space victory". This is, you will not need only to launch the exoplanet expedition, but maintain a system of satellites/space bases to support contact and ensure the success the expedition. The system would require more satellites/bases with earlier techs, and requirements might be reduced with late techs. And you would be able to disable (parts of) the opponent systems with some techs/projects (or maybe even conquering land bases or power sources) . Under certain tresholds, mission will slow down, and even halt. And, if the system reaches minimal dimensions, there will be an increasing chance of "losing" the mission and having to start over (eg. +1% to +5% chance to lose the mission for each turn with a non-operative support system).
Edit:
- added note about airpors in CV.