I don't think this is a big concern. There will still be plenty of demand for Wine even with a decent catalog of Linux-native games. People use Wine for things other than games, and even if tomorrow every single new game had a native Linux port, people would still be playing older Windows-only games for at least another 20 years, probably more.

Also the Windows ABI is still more stable than the Linux ABI. Even if Linux (non-SteamDeck) gaming share went up to like 50% or more, it still would probably be less of a hassle to build for Windows only, the performance difference on Linux+Wine isn't enough to matter.