But did you know Sega actually experimented with a similar idea in Japan for the Dreamcast? Yeah, either did I, but I bumped into this video on Youtube, where the descriptions reads:
I can't think of any earlier cases of consoles letting you download emulated back catalogs of older systems like this (Sega Channel doesn't count as that was for downloading games for the same system). Looks like this would of been another one of those things Sega could have expanded on if the Dreamcast kept going. Another "what if", if you like.