To sum up, proposed changes I'm very confident about:
General
Aqueduct now cost 70 (down from 100). Gold cost is unchanged
Policies Liberty
Meritocracy now reduces unhappiness by 10% (up from 5%).
Representation now also reduces the build time of Colosseum by half.
Finisher now gives a truly free great person.
Additional proposal I'd wish people input:
Monuments and Shrines no longer cost maintenance.
+2 from either Opener, Republic or Collective Rule.
...
Piety Policies
Opener now increases faith by 1 in the capital
Organized Religion now increases culture by 1 from shrines
Religious Tolerance now increases the culture output of Temple by 1
Re: Aqueducts... This may be more balanced, but I feel like it takes away from the flavor of the trees if you have them both explicitly boost aqueducts. Also, it doesn't address the bigger advantage of Tradition, which isn't actually the fact that aqueducts are free and instantly built the moment you finish tradition... (although that's extremely powerful...)
The bigger advantage is that you can skip Engineering (and therefore Construction on Emperor or below) and beeline Education, getting you there about 10 turns earlier. If it weren't for this, Liberty starts could build aqueducts starting on roughly ~t80 while teching towards Education. And with the bonus production, it would go fast. But, having to choose between early education and aqueducts is a big problem, IMHO.
I'm not sure what a better solution would be, but I think the answer is: Aqueducts shouldn't get built for Tradition until you tech Engineering.
This would be a nerf to Tradition, but I believe it's necessary. Because that nerfs Tradition, I don't think there's any need to provide additional boost to Liberty regarding aqueducts. Liberty already gets +5% to EVERY building & wonder, monument/granary/library/aqueduct/university/etc... which I think, in the long run, makes up for the free monuments and aqueducts.
Re: Meritocracy... I think -10% unhappiness is a good idea, but it doesn't address the advantage that Tradition has on high difficulty levels. Monarchy gives an immediate +3 happiness when you get it. Meritocracy gives hardly *any* bonus when you get it. This delays expansion, which is counter-intuitive to Liberty. I would instead add an additional +1 that does *not* require a city connection. (So +2 total w/ city connection) Or, maybe as was previously mentioned, a flat additional bonus upon taking the policy of +2 happiness. (I think +3 would be too much)
Re: fast-build coliseums... I think Liberty's production advantages are fine as is.
Re: Truly free great person... I'm torn. I kind of like the dilemma this creates. However, Great Prophets chosen this way should not affect GS/GE/GM points! That fix alone would make it more useful IMHO. I'm not opposed to the idea of making it truly free, but I also don't see the value in improving one of the best things about the tree. I'd rather see changes that shore up weaknesses.
I truly believe the areas of weaknesses most in need of change in Liberty are happiness and science. So, I continue to advocate reducing the science penalty to 3% with the closer. It's a safe way to make Liberty better IMHO. But, in general, I find Liberty quite strong as is. If they nerfed repairing improvements in enemy territory, then I would say that it needs a slight additional boost. Perhaps a slight reduction in maintenance cost for roads and non-military units? With huge sprawling empires, all those workers and roads become a heavy burden.
Re: Piety...
+1 faith/turn from the Piety opener: This is nice, and solves a lot of the problems with Piety, but one of the big issues is that the *opener* doesn't give culture. Assuming you don't build a monument, with Tradition, you get your first policy on t25 and your second on t33. With Liberty, t25->t45. With Piety, t25->t55. If you build scout/monument, it tends to be more like this: Tradition t17->22, Liberty: t17->25, Piety, t17->t27. But, with Piety, you want to build scout/shrine.
So, I think the *opener* should also give +1 culture from shrines. This would make it less of a compromise to build a shrine before a monument, and you'd get that second policy a few turns faster. (I estimate t33, as compared to t27 if you'd built a monument and t55 if you built neither)
Also, Mandate of Heaven should give a pantheon if you don't already have one. (In addition to what it already gives)
This would create a nice dilemma. Go for bonus faith production or go for a guaranteed pantheon immediately?
This is needed IMHO because Mandate of Heaven, for a 2nd policy, is terrible. It's usually not useful until t80 after you found a religion and build up 160 additional faith. And frankly, even then you often want to extend religion or use a prophet to spread it. So, Mandate of Heaven is a 2nd policy that is not useful until roughly t100. Compare that to Liberty or Tradition, where there are multiple immediately useful 2nd policy choices. And, you'd be forcing a player to make an interesting choice. (A choice which wouldn't come until roughly t30 anyway, so it's not too uber to get that free pantheon IMHO)
This doesn't address the other issues. Piety only has happiness if you invest beliefs in happiness, which isn't fair because someone who founds a religion with Tradition doesn't need to make that sacrifice. Piety only has growth if you invest beliefs, and the same unfairness applies. And the competition for Jesuit Education makes the only science bonus unreliable. One solution, probably beyond the scope of this mod, would be to break down the pantheons into sub-categories (faith, happiness, culture, misc) and allow a Piety player to choose a second pantheon free with Mandate of Heaven, but not from the same category. So, one faith + one culture, or one faith + one happiness. Also, with that second pantheon one could perhaps reuse any pantheon already taken. I think this would allow a player to boost their growth, culture or happiness as needed for their particular strategy. I would nuke the "get the pantheon of the second most popular religion" part of Religious Tolerance though, and replace it with something else. I think if you open Piety, a religion should be almost guaranteed, and perhaps Religious Tolerance could be re-envisioned as a policy that allows you to pick an existing religion (of the civs known to you) as your "secondary" religion, if you missed out on one. You wouldn't be considered the founder, but you would get all non-founder beliefs, immediately, in your capital, including the ability to spawn prophets/missionaries. Thus, opening Piety wouldn't be a waste on Deity in those games when you don't found a religion in time. If this were a random roll and not a choice, it wouldn't be too hard to mod, because it would just be as if a prophet had spread religion to that city. Of course, I'm not sure what that belief would give if you HAD founded a religion though.
Ultimately, Piety needs so much work it's almost beyond the scope of a mod. And, since I'm competitive by nature, I only play HOF games, so I'll never be able to take advantage of such a mod.