Well, lets get real, while the Vita is powerful, the problem besides some tech specs, is that the EmotionEngine has a really complex architecture, we have seen how years it took the PCSX2 team to pull of decents speeds and even needed to "hack" the Vector Unit 1 to make it run on a different thread so they could squize more power of a threaded x86/x64 processor running at 3.0ghz+ clock speeds.
You could get ports easily though, and with them being more similar to their counterparts than PS2 -> PSP ports. Hell, even PS3 ports would look nice, with reduced poly-counts and some particles/texture resolution. You can see that in quite a few Vita games, example of that, being UMVSC3 (look at the hit effects, or the Player bubble when someone is offscreen) or Mortal Kombat (look at the normal maps, low res stuff to almost non-existant on the characters).
It all depends on how intensive the game is too. I can see pretty few PS2 games ported with no quality loss at all. But remember, we're talking about ports. Not emulation. Totally different process.