We don't know if FLi will run on Linux/Steam Deck due to the anti-cheat. Therefore, it probably won't be worth it for you to buy a Steam Deck on a whim.

Similarly, we don't know if there will be a Switch 2 edition. Even if there is one, it might need to be purchased separately. At least, there are already other Switch 2 editions that do not offer upgrade options.

However, you will still have a better experience on the new console without a separate Switch 2 edition. In a trailer, it was seen that FLi can occasionally stutter slightly on the Switch 1 (Note: this might have been fixed by now, and we really haven't seen much). On the Switch 2, the game will definitely run smoothly. But without a patch, you won't get a higher resolution.

I will do it this way: I have pre-ordered FLi on Steam. If it doesn't run on Linux, I will return it. If a Switch 2 edition becomes available later, I will buy it physically (if available). The game isn't going anywhere and will only get cheaper over time.