I would not completely rule out Rare titles on this thing as Microsoft has proven time and time again, they are all about the money. If they can turn a profit, or turn public opinion in their favor by doing something "cool" and make a profit doing it, they will probably do it.
Considering Rare's Microsoft fueled titles have been less than stellar releases, I figure, if Nintendo threw enough money at Microsoft for some Rare titles that it would happen.
Other than that, well, we all know it would not be long before this thing is hacked so having Rare titles won't be a problem for long.