So when are we gonna see a GTA game inside a GTA game?

So I was chatting with some buddies about GTA5 and we were talking about all the side activities that you can do and how detailed some of them are and I had this crazy idea - what if you could play a GTA game inside a GTA game? For example, what if you could take control of one of the characters in GTA5, go into a house, and there'd be a TV with a console there and you could activate it and play a GTA3 game - and I mean like the whole of it. I mean, they ported GTA3 onto iOS, so it's not very demanding by current standards - how hard would it be to just cram the entire game as part of GTA5.

That'd be crazy meta wouldn't it :D

Or has that been done before in GTA games and I just missed it?