I think everything that anyone could suggest would be speculation because no one knows for sure ...
Personally, I wouldn’t be that surprised if there was a redesigned Wii coming out in the not too distant future. This change could be mostly cosmetic for sales purposes (smaller or colours) but it could also incorporate fairly major internal changes to prevent piracy. Before introducing a change like this, Nintendo might keep the supply chain tight so that there were (very) few "old-style" Wii systems remaining unsold prior to releasing the upgraded version.
A more substantial change might also be possible, and Nintendo could do something more in line with the "Gameboy Color" and try to produce an enhanced Wii of some form. If you introduced significant increases in piracy protection while producing a reason for existing owners to upgrade Nintendo could drastically reduce the level of piracy on the Wii. The most obvious possibility for a change like this would be a system that rendered Wii games at HD resolutions, but there are (probably) many other possibilities.
Note: For those that didn't know, in most ways the Gameboy color was identical to the Gameboy and the handful of "Gameboy Color" only games were not released on the Gameboy because color was needed to play the game. The reason I used this as an example is that I think Nintendo would want to keep any new system as being (basically) the same platform.
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