SteamVR has a theater mode. The issue is the pixel density isn't really as high as you'd like it to be. You're using 2160x1200 resolution to render over most of your field of view, so the effective resolution of a rendered TV/cinema screen is actually lower than you might like. It's like playing on a 720p or maybe even a little lower resolution. Also, how will you see your mouse? That's actually not a huge problem if all monitors were replaced there could just be mouse tracking in the simulation.

It's possible, but the resolution and pixel density has to go up before it can be an effective replacement for the amazing screens we have.