I don't get why people think the Vita will be the last handheld Playstation console, the market didn't all of a sudden cease to exist, it's just that Sony has made some pretty glaring mistakes with the system
I think we'll get an announcement of a new handheld from Sony in a year or 2, once they've finished with releasing Morpheus.
Platform holders have to cater to what business there is, so making a new system, with new hardware, righting the issues of the last platform will bring the business back Sony's way, it just needs to be a system without any major obstacles to entry, like being too expense, using expensive proprietary storage and a lack of retail games.
Any new handheld needs to be handled like Sony's handled PS4, being good value, probably with a built in hard drive of some kind, made using tech developers want and most importantly leading the charge with a steady stream of big games to prove the platform's worth to the market.
As for Vita lasting that long, well indies could continue making games for it forever, same goes for those studios that currently support it in the east, but I don't think it would continue on for 10 years from now, maybe 10 years from launch, so another 5-6 years from now, but that would maybe just be Sony keeping the online store live for people to continue buying games from that service. New games will come so long as they sell, but there will be a point when those sales start to take a big dive and all you have is the dregs of like a handful a day or something.
TBH though I think it's more likely that a new handheld with comparable architecture to PS4 releases in late 2016 to 2017. It'd be a scaled down APU with an AMD CPU and GPU tech, along with sufficient memory and a built in HD or just fast SD cards.
