All of that in fully open source drivers? You sure about that? Is it per card?
Ultimately this is pretty much my point, you wrote a whole paragraph about this and I'm still not sure how accurate it is, which cards have which features supported or whether we're even talking about the same thing.
Considering the competition's implementation is "install this one piece of software day one, never think about it again", that is some ways away from a "pretty smooth experience", even without accounting for the parts that are buggy.
For the record, I'm aware of the state of affairs for Nvidia support overall (unfortunately, wish I didn't have to be). I'm gonna say you're wrong about HDR being a driver issue, though, seeing how it was outright disabled for what, three months? due to a showstopping driver bug. It seems to be back to working now, though.
In any case none of this is normie-friendly and an absolute dealbreaker for anybody on modern Nvidia hardware.