It's not completely clear from Apple's wording, but our interpretation of Apple's new rules is that it's likely only the last of those examples will be possible; companies that own the intellectual property could launch emulator apps for downloading ROMs of their (and only their) games. So, for example, Sega could offer a Sega app that would allow users to download an ever-expanding library of Sega games, either as part of a subscription, for free, or as in-app purchases. Sega has offered its retro games on the iPhone before in emulation but with a standalone app for each game… More here.
From time to time I really would like more flexibility on my iPhone and I suspect that in this case it still won’t be particularly useful for most retro gamers. It appears to be half-hearted at best.