So, tried recently (2.6 Hotfix #8), and Rift crashes pretty much instantly on startup. Launcher works, game doesn't. If I set LegacyRenderer to true in rift.cfg, I get far enough to send in an error report, if I don't, I don't even get that.
Only obvious source of concern is that "HardwareDetector.exe" crashed at one point.
I may have some kind of problem with my install, I think one of the DX9 installer things may have failed, except things otherwise seem to think they're installed. I don't know how to check that or reinstall that.