Expired will have to do some updating to make some of these official.
There's a steam version, that I don't believe we can do anything about unless Thal returns to part-time work. I think that's at 3.15 still but I never downloaded from steam.
There's a github version, Expired has full access to that. When he can get to a computer I believe he will update that version with a bunch of bugfixes I found (simple stuff mostly), and that would be at 3.16 still. Those bugfixes are available through the forum here right now (I will be adding in removing the inflation effect as a "bug" as it seems to provide substantial quantities of gold unintentionally).
There's Eric's mod-mod, based off 3.16 I believe, but he hasn't updated it in a while. He has some unique views of balance at times, but may be seasoned to some tastes.
There's Expired's mod-mod which just adjusts the unit upgrade paths (arque to musket instead of arque to gatling) and unit promotion lines (spears are just melee and medic is available to melee units), this is based off 3.16
There's my mod-mod which does a major overhaul to various sections of the game, also based off 3.16 but effectively call it 3.17 as it's very different from the official mod (I threw out a lot of policy and economic changes). I didn't make it a mod-mod, it just overwrites the mod files. I may update these again as I've noticed a few things or come up with some ways to do things I wanted to do, but I would expect they're basically done for a while.
Given that I'm working/commenting on the dll mod and working with Gazebo, one should expect that these would be the sorts of views that I would be pushing for in that balance mod. So far, he seems inclined to take most of the leaders, wonders, buildings, and unit/promotion changes as is from CEP (I don't know if he means my version or the official, but whichever works), and then balance them further from there.
General economic changes, tech tree changes, and many policy changes are still up in the air. And religion changes are a complete mess.