When I bought my 3200, I decided that if Apple development outran Tascam and my drivers stopped working, I'd fall back one version and stay there until such time as OS features were introduced that I couldn't live without. It hasn't happened yet, and the current Mac OS already does a pantload more than I need... I wouldn't feel any need to upgrade if it meant buying a bunch of new gear. (And I'm sure not going Windows... not because it's bad, but because I've been a Mac user for 20 years and I'm not changing now.)
That said, the current beta drivers will likely run fine under 10.10, and then Tascam will post them, I'm sure.