The good news is, whatever they spec it to do will be available to Linux and other OSes because there's really no practical way to spec something Linux couldn't handle as well as Windows without risking antitrust action over something far too stupid to justify such a thing.
The bad news is that people do sometimes do dumb things with keyboards for no reason. I'm using a Dell laptop here. I'm used to the common Fn key on the laptop keyboard mapping the Left Arrow to Home and the Right Arrow to End. Instead this keyboard maps Fn-F11 to Home and Fn-F12 to End. No problem I sez to myself, I'll just map Fn-Left and Fn-Right myself. I've got a number of keyboard customizations already set up anyhow. Alas. The Fn key is supermagical bullshit, and according to XWindows, Fn-Left is nothing. Not an undefined keycap or something suprising... it's just plain nothing. I haven't dug any deeper to see if maybe something lower than X is eating it because I don't care enough (I remapped Windows-Left and Window-Right, retrained my fingers, and called it a day), and I judge the probability that the keyboard hardware is literally emitting no key events for this event too high to be worthwhile.
So, they could spec the Copilot key to be a super magical key that doesn't let you play with others and blocks all other keystrokes while it is held down or something. The good news is, I doubt they'd even want to do that; they're going to want to be able to tell people "Use Copilot+X" to do things themselves, even if they don't have anything for that on day one. They could in principle do something like my Fn key, though, and rigidly insist that only certain defined shortcuts could be used and everything else results in no events, and that is at least an outside chance. Hopefully they don't do anything like that, though, it's honestly more work than just letting it be an otherwise normal key.
cries in Thinkpad
I guess yeah, you can still bind to that key combo and use the key, but you don't get capacity for a "new" binding.
It would be nice if this key somehow was actually usable.