Vita might have a chance in Japan.
It started out a little worst then the PSP but the PSP had a long stretch where it was under performing until Monster Hunter caught fire and developers started porting/creating PS2 games on the system rather then go for the more expensive PS3 or the underpowered DS. It is unlikely to grow that much in most Western territories but it will probably be over 2 years before you can count the Vita down for the count.
The Wii U has less time.
I'd say 20 months depending on how the system fairs once they get more triple AAA titles on it. The fact is, Nintendo tried to be slick, like they were with the Wii and their usual handheld upgrades but failed to have the software or the teams ready to develop them in HD. Now they are scrambling and if they don't pull out of the nosedive they launched the system into with one of their biggest franchises, the only thing they can/should do is declare it a loss and begin the work on the next system that should be able compete better.







