I can see them doing it like the wii U:
Announce it this year at E3, then go into more detail at E3-2015 and release it that winter/spring.
Of course this would work if it was a portable because a shorter lifespan for a portable is acceptable IMO solely because if you look at the capabilities of the vita and 3ds, and the fact that the 3ds is shying away from 3d, a new, beefier non-3d handheld could work great for Nintendo. Especially if that's why we haven't heard anything about cross-accessible VC games.
Then again, this is just my opinion. The lifespan of the DS was ~6-7 years, and the 3DS is nowhere near that old yet, but just announcing it to ensure hype could be a good thing for Nintendo.
Guess we will find out in a few weeks