At the moment PSM games can not have trophies and can not be played on the PS3.
A proper PSN release can have both, and will also have greater access to the Vita's power which is more cut off from PSM games.
At this time we have no idea if this will be a PSN release or just another PSM release with new bits on.
Making it for PSN doesn't mean it has to be 3D...? Minis have a file size restriction so above all, making a full PSN version would allow them to do as much as they want and make as much game as they want without having to worry about that kind of thing. Then there are also added benefits like PSN integration meaning there can be leaderboards (which is something a lot of people wanted in Velocity)
Wait, they can do ps3 games too? :O
I think it would be a 3d game because a psn psm level game or a velocity with leaderboard and trophies would not be that big to deserve a count down imo.