You very likely don't want 10.10 on your DAW or at least not yet. But there will soon come a point where every new Mac will only ship with 10.10 and many others will quickly jump on the upgrade to take advantage of the new features so DAW and audio hardware drivers will have to work on it. It is likely that DAW features will take advantage of some of those new OS features so current audio hardware, new audio hardware, software and drivers all will have to work and work well on 10.10.
When it comes to Mac, most DAW users don't have more than one Mac or a whole separate Mac just for DAW work. I do as I know better than to try and do everything on one computer or base your whole business on one computer, but even with only one Mac you can have access to using more than on OS X version by using an External HD and booting off of that. My main DAW production rig pretty much sticks to released software or Beta software that is in the Release Candidate (RC) stage.