Phil Spencer has very specifically mentioned Mobile devices and PC.
The available devices will be Android, PC, and Xbox for sure. Im sure they want IOS and MAC as well, but that will be if Apple allows it. Remember they dont want a competing store on their platform which is why they declined Steam Link.
As for competing consoles, I highly doubt it. Even if, and thats a BIG IF; If Microsoft wanted it on Sony and Nintendo consoles, they would probably decline it for the same reason Apple is in question. Nintendo declined Rainway, and Sony didnt even like the idea that people would pay for Microtransactions for Fortnite on a competing platform. If you want to look further, remember EA Access?
Im sure people will read into this, but I wouldnt hold my breath. This is highly unlikely to ever happen.