My suspicion is that a company like Apple would want it on-prem, or not at all. A hosted instance with a pinky promise not to peek is not attractive to a lot of large businesses out there.

Your material point may still be valid. Apple could buy it, assuming MS was willing to give Apple a full copy and let them run it internally. (This would require divulging the details of its model to Apple. So I have no clue whether either of them are interested in dealing on such a basis? It would seem like a deal to me if MS could get the right price from Apple? But people a lot smarter than me make that call.)