The Windows Store has updated its policy guidelines for potential developers and sellers. This went down on March 29, but the bit that concerns the emulation scene was only recently spotted by NeoGAF.
The verbiage comes from section 10.13.10 of the lengthy document. It reads, simply: "Apps that emulate a game system are not allowed on any device family." That means no video game emulators allowed on the Windows Store for Windows 10 PCs, Xbox Ones or devices running Windows Phone.
Look elsewhere for emulation
Now, I'm not condoning you run out and pirate games; however, there's a side to emulation that I am completely in favor of, and it's one that our own Ron Duwell hits regularly in his stories. That's emulation for the long term preservation of games. As we transition away from physical media for our video games, it's going to become nigh impossible to find classic games as the years roll on.
Do we leave it up to publishers to take on the burden of preserving games? No. First of all, I doubt they want to. Second, not all publishers stay in business. They shut down, and then the games will be gone for good.
There are better emulators out there than what were on the Windows Store. Look elsewhere, and do it for preservation.
Most who emulate games probably don't need the Windows Store
I get why Microsoft banned the emulators from their marketplace, but we all know it's likely not going to put a dent in game piracy. Gamers have been emulating for well over a decade now. Even longer, really. As long as personal computers have been a thing, gamers have been using them to emulate arcade and console games.
Heck, I can remember firing up MAME to play Marvel Super Heroes vs. Street Fighter around 1998 or so. We did it in Computer Lab, no less!
My point is this: the folks who emulate games know how to get around platform-based marketplaces. It makes life a little harder on consoles and mobile devices, but there's likely already a workaround for that.
Microsoft would be better served banning shady and broken apps than emulators, quite frankly.