As much as I would love a Vita 2 or whatever, its not really needed right now and going head to head with a new Nintendo handheld is probably not going to end too well.
Vita is still ticking over nicely with lots of games, sure its not really selling millions like PS4 but for something Sony is not really doing anything with, its getting enough good games still. If it ever happens, it wont be for a long time. Sony has got all its focus on PS4, PSVR and Neo, so the support wouldn't be there for it.