SteamDeck "success" is still out there to validate.
Doesn't have the sales of any Nintendo handheld that has earned its place on history books, and remains to be seen for how long Microsoft will tolerate Proton as Windows/DirectX translation layer.
I think the window for Microsoft to squash Proton (if that was ever practical) has already passed. Valve will be able to stand up to any litigious bullying and they have financial incentive to do so. And defeating it from the technical side with a new interface would require buy-in from developers, which Microsoft has consistently been unable to obtain.
Doesn't have the sales of any Nintendo handheld that has earned its place on history books, and remains to be seen for how long Microsoft will tolerate Proton as Windows/DirectX translation layer.