It'll probably turn a division of Microsoft that usually loses money into one that loses...more money.
From Heroic's FAQ, that's the first step for adding support to the store.
https://github.com/Heroic-Games-Launcher/HeroicGamesLauncher...
Not exactly first class, but one step away.
The SteamOS is capable of getting out of the way, which is something Microsoft is pathologically incapable of designing Windows to do. And these days I think Linux and the Linux desktop are just objectively better than Windows, and the days where Windows embodied what it meant to have when anything goes PC are long gone.
So you're left with limited options. I think a first class console experience for a wide range of storefronts is the best bet to out-steam Steam but it assumes a degree of execution capability that I don't trust Microsoft to have.