Actually... capcom released Monster hunter portable 3rd on the greatest hits line around the same time as 3G came out.
I dont think theres anything coming until after Monster Hunter 4 comes out on the 3DS. Thats what the team is working on afterall... best case scenario for the Vita is a simultanious release or a later port.
You have to think about it.... if capcom were to release a MH title on the Vita in Japan, its main market, it would be looking at 600k sales if it sold 1 to 1... thats not gonna happen so an optimistic prediction would be 200k-ish sales. Does it sound worth it? Doesnt to me when they can release it on the 3DS and get above one million sales.