imo the 3DS hasn't really stolen the PSP audience. Maybe a little, and they're slowly moving over, but I think most of the PSP audience is still on the PSP. The Vita didn't convince them to move to that and the 3DS hasn't really either though it's looking better every day. If they move to the 3DS it'll be because Sony fucked up the Vita and not because Nintendo was able to "capture" the PSP audience. I don't see the 3DS ever getting the sales for certain series that PSP got.
I'm not even sure how Sony screwed up the Vita so bad in Japan. Was it priced too high? Maybe a little, should have been about $50 less. Was it too confusing for the consumer? Probably, should have just been 1 model. Were there no Japanese catering games? Sorta, I mean there was Minna no Golf, Tales of Innocence-R, Dynasty Warriors, Gravity Daze around launch but it definitely could have used a few more Japanese titles.
Those all seem like mistakes by Sony, but not major SYSTEM WILL DIE mistakes, but rather just enough mistakes to not be a great launch. However, the system is dying. But yeah, I dunno how they could/will fix it. Zero no Kiseki full voice edition should have been launch window though. Sony should have worked with them on that since it's just a port with voice + some goodies and Kiseki is fairly popular now and fills a gap on the Vita.