The idea of multiple games affecting each other is something that EVE creators CCP are experimenting with in Dust 514. For a long time I had been thinking of a Mega Game. A game that was persistent and had everything in it. MMOs covered part of it, and FreeRealms kind of did what I wanted. I haven't tried Lego Universe yet, but it seems to have a nice variety of activity in it.
No, a Mega Game is about being all games tied to a single Avatar. You would make your Avatar, and control him in a persistent world. This world would have adventure and hi-jinks. With this same character, with the stats and choices you make, you can then switch over to racing, fighting, puzzle combat, crafting, etc etc. Your choices in appearance, and stats would affect the other aspects of the game. So high agility or intelligence would give you faster acceleration in the racing game or strength and intelligence would give you a better top speed. Your car would look a certain way based on your gear and appearance choices (details were never figured out).
The other idea I've been hoping to see (or later on create) is a true Multi-game. Where I could release a city building Sim to casual players, which in turn becomes cities used in a strategy game. The cities layout would be used for when a unit invades an occupied city. The game would then become a Tower Defense style game.