As far as the big, mainstream consoles go, the original Xbox only saw four years on the market 2001-2005 before being replaced. I think Sega Saturn was also on the market for four years as well. There's definately a presedant.

N already sold 8 million Wii U.

6 million till 31 December 2013

Like usual, after 5 years from Wii U strat there will be new N console, but it is normal for them.

The GBA to be fair wasn't really intended since the DS was at first designed to be third system go alongside the GBA and the gamecube. Its only after it sold well that Nintendo decided to get rid of the GBA and focus everything on the DS. 

The Saturn had four years in Japan and Europe, however only 3 years in North America.

My bold prediction: Your prediction is wrong.

Hahahahahahahahahaahahahahaha, no. Seriousily, no. This won't do any good.

If it does happen again, where do you think things will go?..I mean, crossing fingers they´ll really learn from the Wii U mess, and be able to have a successful product next time....but, if things don´t go well again, what do you think might happen/will happen?

I can't see how MK8 and SSB could be "huge commercial flops". Even if they both sold relatively badly (which would be rather surprising), there isn't really anything about them that suggests they cost a lot.

Also don't see your 2015 prediction coming true. Nintendo aren't stupid, they know it'd be better to squeeze as much out of the WiiU as possible before killing it off. Not to mention discontinuing a console that soon after launch would hugely damage their customers faith in them.

WiiU just passed the 6M mark, ~1 year and half after being released and you say it can only sell 3 more millions until the end of this year?!!

Wait, makes sense....