Some ideas I have for modcomps (may not be unique to this thread, sorry, I'm not going to go through all 12 pages):
~increased movement of naval units and especially embarked units... especially mid-late game. I'm thinking techs like optics, astronomy, steam power, combustion, and fission could give movement point boosts to both naval and embarked units. My reasoning that it would give movement points to all units is that even sailing ships were retrofitted with the engines of the day once they came out (steam frigates, etc.), and primitive rowing vessels were retrofitted into the first ocean-going sailing vessels, etc. Also, probably with astronomy or optics (can't remember if this already happens ingame, know it does in earlier Civ's) all vessels can venture into open water.
~rivers are trading routes either with sailing or on opening... coasts are trading routes either with sailing or with optics... oceans with astronomy or with optics... all cities connected by trading routes by completing some national wonder (Spirit of St. Louis, etc.) with flight as a prerequisite tech.
~bring back airlifts
~break up unit types so that I can station, say a artillery, ranged, and melee unit on the same tile. Technically what I'm thinking is to break it up even further, sure, artillery, ranged, and melee, but also mounted (or mobile, which would upgrade to tanks and armor), the melee would be "infantry" and would upgrade from early melee to gunpowder units, and ranged would start out as archer units and would upgrade to sniper units or something like that (which is probably another modcomp idea in and of itself, I admit), and then there would of course be helicopter units on their own in the modern era, maybe lancers could be put into a class with them, I don't know.
~some better late game units, especially air and naval units. As it is the air and naval units don't really advance much past the 70s era of units... there's no stealth fighter, drones, supercarriers, amphibious assault vehicles, stealth naval vessels or stealth anything except the stealth bomber and really its not very stealthy. I know its a game, but just having the only very late game/future era unit of note be the GDR is sort of boring to me. Even without going all hyperfuturistic there's plenty of potential units that could be added. I mean, even if, for instance, there's a wonder that comes with the stealth tech that automatically grants all pertinent air and naval vessels the stealth promotions (basically making all your jet fighters stealth jet fighters)... that's another way of putting the same late game twist in, though I still think having the option to build some of these units should be there (like Supercarriers, etc.). Maybe even have all jet fighters and missile cruisers, destroyers built after stealth is discovered automatically get the promotion, too.
~change the minimum damage value on the combat system from 1 to 0. If its as easy as I think it is I would hope that would be added into every mod ever done in Civ5, just for the sake of thoroughness.
~maybe have a tactical nuke unit that is basically an artillery piece and blows up a single tile within three tiles of the gun, with one or two random tiles adjacent to it getting hit with fallout (and any exposed units or cities in those tiles getting some, but not terribly bad damage as well, sort of an incentive for not using the thing right next to you). It's why its a "tactical" nuclear weapon. Though the idea of the thing blasting away one tile with 1UPT makes more sense when you add in the multiple unit types sitting on the same tile thing (as many as four or five units on the same tile as some sort of "army" that gets blasted to oblivion in one shot, not to mention tactical nuke could even be some sort of unit you load onto a regular artillery unit and fire from there, who knows?)
~on that note, why not have missiles, artillery and bombers/jets be conventional for the most part, but you can build and load nuke/wmd packages that they deliver, that way you can use a stealth bomber to nuke someone or use a cruise missile to nuke someone, or even just build conventional ballistic missiles, etc.
I've probably gone through way too much here. By the way, not really saying all of this should be made into one mod but each thing is its own thing together (i.e. mod-comp). Just have a whole lot of ideas.