I don't know if the 7800 needs to be on it's own or just add it along with the 2600 flashback like the whole backwards compatibility of the 7800.
I would add it along with the 2600 offering. While a separate 7800 flashback would be cool, it just doesn't have the clout nor cache the 2600 does. However, putting them in addition to 2600 titles (say 20 7800 and 120 or more 2600 games) would probably be something AtGames could feasibly do.