My Steam Deck will arrived this week and the FIRST thought I had, was to use it for my arcade cabinet. I could easily 3D print something so I can add a dock on top of the arcade - just drop in the Steam Deck and voila, the screen, iPac, etc. are connected. It seems like a good marriage to me.
However ... Valve has said many times it won't give Windows support, probably because they want to push developers to add support for Linux or to make it work properly using Proteus. Frankly I think they WILL add Windows support because they'll find the demand for dual booting will become quite big and they may find that Proteus won't offer enough compatibility compared to Windows. ETA seemed to get Windows to work rather well compared to LTT who basically said it was an incredibly rough experience.
So yeah, it's a bit of a gamble - do you develop for Linux and then find out the Steam Deck will get proper Windows support after all? Or do you just develop regardless of the Steam Deck, knowing you'll at least have a Linux alternative? Maybe a poll asking if people would pay for an extra Linux version would shed some light but even then ...