Thought I'd register an account to give some personal experiences with how the AI acts with the available but incomplete civs from this thread. (This is on Prince, I'm not sure how the AI would behave above that, but I assume it's similar.)
Hey, nvdr, thanks for the feedback! I generally play on Prince myself, so do most of my testing at that level, although sometimes I play at Warlord to break in a new civ the first time, just to make sure everything's working without having to deal with the enemy AI as well.
Makai: I haven't noticed any issues in terms of their performance, and they've always been good about using their improvement when they can. That said, they do seem to fall a bit behind but that could be the difficulty.
I've noticed them using their improvement as well, so it seems that it works well enough to entice the AI into using it. In my last game (playing as Yuuka) they were a bit behind in the culture race but appeared to be gaining ground when I had to stop, so hopefully they'll be adequate in that regard. I'm not entirely sure how well the AI does in trying to build up tourism, but I know there are cultural civs... maybe I'll have to set Shinki's flavors to something similar to Poland?
I've also modified the UA since I last posted the civ, I think -- the UA now starts spawning free military units based on the level of tourism in the civ in the end game. This should hopefully enable her to warmonger against anyone that doesn't capitulate to her tourism influence.

I need to tinker with the spawning rates a bit more, though.
Tanuki: Haven't actually had them as an AI often enough, but they seem to do fine. (There was one time in a game with nothing but domination available for victory where they got destroyed really quick, might have been them trying to use the UU like normal units?)
They seemed to be doing all right points-wise in my last game, with Germany constantly trying to agitate for a war against them. In a previous game (testing as Makai) they were actually decent warmongers, going to war against a couple of other civs. The Trickster isn't really any worse than the Scout in combat, and the AI isn't smart enough to take advantage of their unique ability, so they should just be using them as scouts. But since they're a mid- to late-game civ (their UA really doesn't kick in until the Renaissance, as does their UB), I do wonder if they just got taken out by an aggressive early-game power.
Still, as they do seem to be doing adequately, I'll likely try to get them published soon, once I can find some time to do a final debugging.
Yuuka: She seems to have done totally fine in the one game I played with her so far, although she had no nearby neighbors. However, by turn ~250, by the time I got a unit down there to look around, I found no evidence that the AI built the sunflowers at all. (Unlike the moai spam I've always seen Polynesia do.) There might need to be some sort of yield change if the AI using it is intended to happen.
I suspect the AI emphasizes Food, Production, and Gold output -- with Moriya, I noticed the AI wouldn't bother with mountains, even if they had science, culture, or faith outputs, unless they generated food. So the AI probably would always prioritize farms over sunflower fields. Not entirely sure how to get around this, aside from possibly forcing the AI to replace farms with sunflower fields on occasion. As Huitzil noted, once you get a few going they seem to become more attractive to the AI, as it realizes that the culture yields are big enough.
Moriya: while they are up on the workshop and everything, I thought I'd note that they seem to not care about settling near mountains any more than any other civ, although there's probably no way to change that. They also seem to override the workable mountains mod, making other civs unable to gain the yields provided by that mod. (That said, if they got those yields themselves they'd probably be OP in mountainous areas.)
Moriya is actually due for an update, so thanks for the reminder! I'm pretty sure I can revise the UA so that the bonus from mountains is a passive effect, rather than needing the tiles to be worked, so it will avoid conflicts with mods like Workable Mountains. Most likely I'd tone it down to something like "Cities get +1 Science and +1 Faith for each mountain tile in their radius". It would also make for a nice early-game bonus, as you could simply settle near a mountain to start reaping the rewards. I know from some feedback that their abilities really only start kicking in in the Classical era, once you can get Taishas going, so being able to give them a minor faith and science boost to get to that point would be good. At the same time, I do have to tone down the Taisha's yields a bit...
Also, is there any chance of a Venice style touhou civ happening? I've always liked the concept and there's bound to be someone it could work for. (The Taoists or Myouren Temple perhaps?)
What do you mean by a "Venice style civ"? I assume you mean a "one city challenge/OCC" style... which, I'll confess, we hadn't really considered yet. X3 I suspect part of the issue is that most of the characters that are appealing for civs lead power blocs, which would seem to suggest growing/expanding civilizations.
Huitzil and I had talked about Myouren Temple and the Taoists, although we've largely agreed that they'd be civs focused on the diplomatic victory through city-state manipulation. Arguably, either could be done as a OCC civ, which would expand through taking over city-states -- Miko, for example, could potentally add a city-state to her empire by fulfilling a certain number of city-state quests.

But even that could simply be done as part of a normal UA, like Austria...
For a OCC civ, my thoughts would lean towards either the Hakurei Shrine, or the kobito under Sukuna. The Hakurei Shrine has always been a difficult one for me, because it's hard to figure out how to reflect Reimu's archetypal laziness... but an OCC civ does seem like an interesting possibility, forcing her to expand by beating up and defeating the various youkai. Given that the kobito have almost entirely vanished, I think they might be a good alternative candidate for OCC, particularly since the Miracle Mallet could easily reflect an enhanced Palace.
Anyways, thanks again for the feedback!