Emulators, long forbidden on the App Store unless baked in to a single app or game, may finally do what they're good for: downloading, storing and running retro games, apps and other software written for the emulated system. It comes after the European Union made Apple loosen up a little and comes with a large caveat. Check out the exact wording of the new policy:
4.7 Mini apps, mini games, streaming games, chatbots, plug-ins, and game emulators
Apps may offer certain software that is not embedded in the binary, specifically HTML5 mini apps and mini games, streaming games, chatbots, and plug-ins. Additionally, retro game console emulator apps can offer to download games. You are responsible for all such software offered in your app, including ensuring that such software complies with these Guidelines and all applicable laws. Software that does not comply with one or more guidelines will lead to the rejection of your app. You must also ensure that the software adheres to the additional rules that follow in 4.7.1 and 4.7.5. These additional rules are important to preserve the experience that App Store customers expect, and to help ensure user safety.
The funny but perfectly understandable implication is that you can put the emulators on the store now, but your emulator can't download the ROMs unless they're your ROMs. So, if you're thinking "MAME for iOS" you'll be disappointed. If you're thinking "Sega Collection where you can buy and add every Sega game ever" you're good.
Previously: A cheap and easy retrogaming console
