Vita just launched, they wont announce all their big guns right away. They`ll have the announcements when it makes sense, probably after that launch period. As you said, they have been working on Tri G for 3DS since late 2010, but they didnt announce at the 3DS launch or even when the system was selling like crap after its launch period.
No matter what happens, i hope that the Vita will get its fair share of exclusive software and that it doesnt all will run into HD ports ala FFX or MGS collection.
The day 3DS was announced Capcom announced Megaman Legends 3, Resident Evil: Revelations, and Super Street Fighter IV. When Vita was formally brought out, Capcom announced Street Fighter x Tekken. Capcom's PSP support was pretty crappy (a few weeks ago I did a round up and something like 60-70% of their PSP lineup consisted of a port or remake), but their Vita support is even worse in light of their 3DS support.