The problem is that W8 already had troubles penetrating the market and the app store is doing even worse. It's complete wasteland. If what you mean is closing down the whole OS in Windows9, not allowing anything to be installed that's not bought from App Store..well..that would essentially kill the whole OS. People would just stick to previous versions and gamers would slowly, but steadily, start to move towards Linux thanks to Valve's efforts.
It would bassicaly be a suicide and all for what? An attempt at capturing the already sunsetting console market?
Now, I do think they might get a chance if they decide to compete on even level instead of trying to cut out the competition. Bassicaly imagine if they just release mobile and Xbox games on Windows Markerplace, as the "buy once, play on 2-3 devices" kind of deal. On PC you could still buy from other vendors, but Xbox games would be avaible solely on Marketplace. And on console that marketplace would be the only thing that exist. That would be nice incentive for people to buy there, while avoiding the disastrous consequences of closing the OS.