Looks like they'll need the PS3 and PSP to carry them in Japan until a Japanese killer app comes out, and even then without a Monster Hunter it seems the Vita is a lost cause in Japan. I'm hoping western sales for the Vita aren't as poor, but judging by the constant doom articles in regards to an obligatory $20 proprietary memory card compounded on the $250 price (a price which was once deemed cheap at E3), things seem grim.
MH tri G must be a hell of a game, because I'm currently playing FE: Sacred Stones and Pushmo on my 3DS. MK7 was just a tad underwhelming in comparison to MK DS which I believe was reflected in its critic scores. Granted i'm no advocate for 'professional' game reviews. Also shameless advert, if you have a 3DS buy Pushmo.