Well, they can either sit on their hands having every cross platform title look and run better on PS4 or they can try and come up with a solution. If they offer an improved console that runs all the same games, but any new games will comfortably play in 1080p60 then I think that could be an easy sell. Like the Slim revision of the 360, but actually with better hardware this time.
It's a bit of extra work for devs, but certainly not insurmountable. They basically stipulate that every game must run on both, but on the Xbox One S, you've got a bit of extra grunt to play with to offer a smoother and/or higher-resolution experience.
This already happens on iOS.
I think so long as there is never a game that simply won't play on the vanilla Xbox One then this could be a great idea. I'd buy a beefed up Xbox One in a heartbeat.