What do you guys think?
I think that porting one game to another platform is not a simple task, and can actually do more harm than good depending on engine, development resources and overall ROI. You would not see as much focused publicity if it were a multiplatform release (SCEJ conference, PlayStation Experience...) and, as you suggest, the majority of fans who would get Persona 5 are most likely on PS3/PS4 as opposed to X360/XONE.
Also, as atlusprime suggests, the primary market for the game isn't hot on Microsoft consoles at all, which goes back to my first point.