All in all arguing what development tools and engine can work when and where is moot as its basically a hypothetical tug of war between those who want it to be on the Wii and those who absolutely don't.
In the End, the Wii is the prime choice, no one can argue that. Does that mean its garanteed to go to the Wii? No. But you'd have to be a fool or overly optimistic to think its not the prime candidate.
The hesitation to announce the console could be the result of two things, 1. there is a power struggle between Disney and Sony/Square-Enix over what platform to put it on, or 2. Square-Enix, like most developers, are waiting till MGS4 is released before deciding whether to commit fully to the Wii.
I think the later is more likely, in fact, I feel most likely that every major Eastern developer wants to support the PS3 over the Wii but are hesitant and its not unthinkable that MGS4 would be the real deal breaker as to whether the Wii or the PS3 is the viable console for their flagship games.