Yeah, but the backend seems to be buggy, the documentation is not up-to-date and basically half the things that work in 3.x break mysteriously in 3.(x + 1).

Meanwhile I can use a gtk2 theme from 2006 without any problems (and it doesn't make my desktop look like a kid's HD drawing). As long as I can do that, I have very little motivation to put up with gtk3's crap.