Unlike the PS2, the PS3 does not suck at using the internet. And it has a reasonable hard drive. So it's possible that addons aren't out of reach for PS3 players. Just a matter of finding a way to deliver them without making them want to jump off a cliff.
I'm thinking some variation on an app market that could integrate with the game client itself. That would also have the advantage of letting SE decide what addons they do and don't want to exist.