Let's see:
1. Wii is by far outselling anything known to man. (gaming wise)
2. Godfather Blackhand was amazing on the Wii, controls FTW!!
3. GTA is a better game thad Godfather.
4. GTA4 was initiated years prior to Wii, therefore the only reason it isn't on Wii now is because of how badly Gamecube sold.
5. Rockstar/take two have already been showing Wii some love from "mature" games like Bully and manhunt 2 to games designed solely for higher end machines like Table Tennis.
6. Rockstar/Take Two are a company that last I checked wanted to make money. When GTASA had already made them a brazillian dollars on the massive PS2 they still later ported it to the Xbox.
Oh, GTA4 may not make it to Wii due to size constraints, but there is not reason they won't scale it down some and put it out on a Wii. They can't ignore the millions of Wii owners. They would be financially stupid to.
I would bet for a GTA4 knockoff that was built specifically for the Wii at the least. Godfather type controls, if not better, and really nice graphics. Possibly will be rated as best looking game on Wii. Then BAM!!!! Wii sells hit next huge rush as all the little teens run out saying Nintendo is no longer kiddie!!!!