Currently on the Wii, the Vita would be the system of choice in japan as due to their favour towards portables. The Vita is not only powerful enough to maintain the visuals, it will allow for improvements.
DQX will not be only on Wii but with better graphics on Wii U too. There is not the slightest chance that Dragon Quest goes to Vita, a system that called dead from most japanese developers. It will be Wii and Wii U exklusive, perhaps later on a 3DS version.
Its seems obvious that a portable COD would be a massive success
Obvious? No. COD games are for the big consoles not for handhelds. By the way: The DS got some CoD-Games. I think the 3DS will get some too. And the Vita will get a CoD-Game if the sales get better in US.
The only things that would save the Vita are a much lower price of Hardware and games. And a bunch of good games. But none of that is beeing in sight.