It's definitely a concern. While Valve state the goal is to have 100% of the library playable, I'm aware of how ridiculously big an ask that is, & I'm not expecting it at all. Realistically, I'm expecting 75% of my games to work & work well. Anything less than that would be very unfortunate. If they manage anywhere in the 90-100% range I'll be blown away... Ahh, I just want it now! The 3 month wait is killing me!
(Whatever the case, I'm still going to download every emulator under the sun, so I'll have plenty to play whatever happens
A lot of games I enjoy also have native Linux ports anyway, so maybe it won't be a big deal).