The most concerning detail for me is how to acquire the rights to the ROM.
Can anyone who legally purchased it upload an emulator of a popular game to the App Store?
Only time will tell but the article notes that it is likely that this change is for publishers, not for end users.
I doubt that we are going to see many third-party emulator because of the ROM issue. To my knowledge, most consoles and all computers will have copyrightable ROMs built into the system. Given the relative scarcity of old hardware, equipment, and technical skills to image those ROMs any third-party emulator will attract copyright infringement. That is before you consider imaging software. (While there is a good chance that a person can retrieve a working mask or EPROM from an old system/cartridge, anything disk based will be much more sketchy. Not only do you need working drives to image the software, you need working media and the media cannot be copy protected.)
With the caveat that some emulators need BIOS files or decryption keys pulled from the original system, and you can't redistribute those even if you only intend to run free homebrew games.
And the last time that was tested with Connectix and Sony, Connectix won in the end but faced so many legal fees they still had to end up selling it to Sony and abandoning it.
Sure, and companies could also sue you for libel when you leave a negative product review. Life is unfair, but when talking strictly about what's legal or not, homebrew roms using an emulator that has a clean room implementations of BIOS should be perfectly acceptable for the App store legal-wise.
Why can't you redistribute those? You cannot copyright a key. If I bought a console and somehow manage to extract the keys, what exactly prevents me from distributing them?
If you're in the US, or the place you're trying to distribute to is under US jurisdiction, the DMCA is what forbids you from distributing DRM decryption keys. That's why emulators for modern systems usually don't include the keys, and make the user provide their own copy of them.
Unfortunately if you want to publish on the App Store or the Play Store then you have to play by the US rules, regardless of where you are, since Apple and Google operate out of the US.
For example, ScummVM for iOS includes the MT-32 emulator MUNT. It doesn't bundle images of the ROMs in the MT-32 (which would be illegal without license from Roland). Instead, the user can dump the ROMs from their own MT-32 or obtain them by some other means and drop them in the app data folder themselves.
I doubt that we are going to see many third-party emulator because of the ROM issue. To my knowledge, most consoles and all computers will have copyrightable ROMs built into the system. Given the relative scarcity of old hardware, equipment, and technical skills to image those ROMs any third-party emulator will attract copyright infringement. That is before you consider imaging software. (While there is a good chance that a person can retrieve a working mask or EPROM from an old system/cartridge, anything disk based will be much more sketchy. Not only do you need working drives to image the software, you need working media and the media cannot be copy protected.)