I'm putting a pretty safe bet on it being restricted to ROM loading, because if they have the potential for all the same functionality, I'm not sure why they'd tell people on 4.x to stay on 4.x.
Could be if they have an exploit, it's more of a hassle to use. We already know the profile exploit is gone, so if they have another, it would need another entry point. So if for example it was something like a save exploit/game exploit, then it would still make sense to stay on 4.5, as running the profile exploit is far less hassle, than booting a game, exploit, then swapping to the gateway