It doesn't matter is it service or not, Sony SPECIFICALLY blocked God Of War to be played on Xbox. There is no native GFN app on Xbox, but it can be played via web page, yet Sony blocked it when there was a native version on GFN.
Yes. Those who owns a whole librabry of games on Steam or on Epic etc. can be played via GFN, but not Sonys games who bought them on these stores. Still haven't find any damn video of Spiderman played via GFN, yet Spiderman is available on Steam and Epic store
Simple answer is NO
Which is exactly what I said: they blocked GFN in total (or better to say they told Nvidia to remove their games), not only on Xbox.
Or release their own launcher where they can control everything about their games
Doesn't help if it's possible to install their launcher on the next Xbox....