The Wii is Nintendo's most successful console by leaps and bounds. It would be a mistake *not* to include the Wii name after a hundred million or so sales.
The 3DS was poorly advertised and poorly placed (i.e. 3DS games were mixed in with DS games at stores). When I went to buy an iPhone, I certainly knew the difference between the 4 and the 4s, despite their relatively minor upgrades (certainly the aesthetics were exact). Although I am an informed consumer, Apple certainly made these differences known via advertising.
Am I confident that Nintendo can hit it out of the park advertising the 'new' Wii? No. But to discard the success behind that name would be crazy in my opinion.
This would be better in a name standpoint but worse from a brand confusion standpoint. Wii-U at least shows that it could be something new, but Wii Entertainment System could make people think that name is just the "long" name for the Wii.