Which I imagine it will be at some stage.
Will it? I'm sincerely curious whether or not the Vita actually has that kind of power. It can't even emulate past generation Dynasty Warriors games without severely cutting corners by limiting the fields or drastically cutting the draw distance. From what all I remember those are pretty comparable because while Disgaea doesn't use 3D models or anything, there's supposedly a lot of power being drawn from the console's hardware for calculations, enemy counts, ect. (I seem to recall even as something as basic as D3's tower-based antics had to be done on a PS3 because the PS2 couldn't handle such things alongside the massive amount of data calculations a Disgaea game requires; despite all being 2D Sprite-Based.)
Currently to back this, Disgaea D2 dropped about 2 years ago and there hasn't been a single peep about a Vita port for that. Making me think there's some reason it can't be done until we see whatever the next Sony handheld is.