I think 3 thigs need to happen for the Wii successor to get the type and amount of support similar to the HD consoles or the PS2 the gen before. The 1st has already happened, the Wii is a success and Nintendo has shown they are still able to sell an extensive amount of home consoles which was in question after N64 and Gamecube. 2) The 3DS needs to be a hit and the big name games (Resident Evil, Street Fighter, MGS, Assassin's Creed etc.) need to sell well, proving 3rd parties can sell on Nintendo consoles if they bring their big guns. 3) The Wii successor needs to be technically similar to the competitors. It can still be the weakest, but needs to be like the PS2 compared to Xbox as somebody said earlier.
I think if all those things happen the next Nintendo console will see its most 3rd party support since the SNES.
I also think there are few more minor factors that could also play a role, such as how do the few big budget 3rd party Wii games do for the rest of the gen (Epic Mickey, Goldeneye), and if the the Wii succesor is the first next gen console to launch that could also be a big help.
