So what we know
-Addictive, can play for hours a day
-Third party
-Not Indie
I am going to guess that it is Grand Theft Auto San Andreas Stories. Shouldn't be hard to make. They can just reuse all the assets from the original. Also Rockstar has experience in making for making GTA on similar architecture as GTA3 and Vice City have released on iOS and Android before. Why do I think it is San Andreas Stories, because this is the cheapest and quickest way to get a big 3rd party exclusive on to the Vita (reusing assets, reusing engone from iOS/Android GTA's). GTA also fits the description of addictive and can play for hours wrecking havoc in the sandbox. Also with the release of GTA5, this is a good time to announce this as well. Another game it could be is Type 0 HD. Basically I am going to keep my expectations low, I beleive no 3rd party is going to release a big game exclusively on the Vita as it doesnt make financial sense. So games were they can reuse assets, HD ports and etc is where it makes sense (GTA San Andreas Stories, Final Fantasy Type 0 HD).