I believe wine has a WoW64 implementation now, to allow 32 bit software to run on 64 bit wine prefixes. Which means any windows games (unless they are 16 bit) can work on 64 bit non-multi-arch system.

Linux games are the core problem. But they also have a Steam Runtime where they ship the entire runtime libraries needed to run a game for compatibility reasons... and Steam Runtime 4.0 (which just shipped and/or announced a few days ago?) is set up for only 64 bit systems.

So if the answer is:

• Steam itself can be 64 bit, and is moving that direction
• Windows games can be 64 bit only due to proton/wine handling the 32bit translation in WoW64
• Linux games themselves can be any architecture since the steam runtime manages the libraries for the games.

Then the answer is just "they're getting around to it, they are only just now getting around to it for windows, and linux is a lower priority" because clearly its all possible.

So "What about linux?" is just asking if there is a timeline for the speed that things are moving in that direction.

Running Steam should be fully independent of running games.

At least the client. You might still need some 32-bit libs if a game uses steamworks drm. I'm not sure how stuff like the overlay or achievements are integrated.