I think you need to temper your expectations of early next gen games.
My argument is that pretty much anything can scale to a degree from resolution to physics and AI. It should not be mandated since games could use something like advanced physics as a core concept, but in general pretty much any game made this generation could have been a last generation game if toned down enough. The same will be true next gen - no matter how many Xbox first party games runs on Xbox One. How long it is worth having the goal of running on Xbox One would obviously depends on where people play the games.
it isn't about mandates. It's that 1st party games have a very specific mission at the start of any generation; to convince gamers to buy a machine to play it.
Further, due to backwards compatibility being present for both sides, third party studios absolutely has no incentive to release next gen titles at their maximum capacity early on. So the only way for a next gen console to showcase itself at launch, is from 1st party games that are intentionally made to "show off".
So to not have Scarlet exclusives at launch, if true, would hamstring Microsoft's ability to market their console.
Now, for many posts i have been arguing with some here who believe that this is fine, that Microsoft doesn't need Scarlet to succeed and that next gen console isn't important anyway. I am not sure that person is for real or trolling, but at some point it doesn't matter.
And it bears repeating that this could all end up being just a badly written article using rumor that end up being misinterpreted. But none the less we are a forum and discussions are fun.