Why do you think apps wouldn't be compatible? It would be just like Amazon - yes, you'd need to run a new store (fairly trivial for an MS or Nokia type org to get going) and need a new billing API, but that's all you'd need to get going.
To put this in perspective moving Play Store builds to the Amazon store is generally a matter of replacing the billing and push APIs, if you've used them, which takes a few hours. (If you've used game services it might take longer, but again it's not actually hard). This is far easier than redeveloping your app completely for a different platform.
I've been involved with apps for which the move to Amazon was simply a 10 minute boot up on a Kindle Fire to establish it worked.
Nokia are bad at it, but you might recall the N-Gage that had a services layer that wasn't completely terrible. In Europe the operators usually ran this stuff, at least pre-Apple/Google, and there were a good few companies that existed by selling portals which were white labelled and branded as the operator stores.
These things certainly can be killed in bureaucracy, but the tech issues aren't too bad, especially if you're already sitting on a giant pile of servers and a billing solution for each country. At one point I knew one team running stores for about 20 operators (each country is essentially separate) with less than that in developers, and only a handful of sysadmins, if you can have such a thing.
To put this in perspective moving Play Store builds to the Amazon store is generally a matter of replacing the billing and push APIs, if you've used them, which takes a few hours. (If you've used game services it might take longer, but again it's not actually hard). This is far easier than redeveloping your app completely for a different platform.
I've been involved with apps for which the move to Amazon was simply a 10 minute boot up on a Kindle Fire to establish it worked.