The PS4 and Xbone versions won't be released until those systems launch (at the earliest), which will be after the launch of Swap Force. They refuse to say anything about those versions, like what improvements will be made versus the current generation versions, so who knows what'll happen.
It starts off simple enough, but there are many places where the difficulty is just unreasonable or downright cruel. And yeah, you can't save until you beat the game, except for a few levels (like castles). So you end up beating the first castle level over and over just to save your progress.
God, NOA sucks. I imported this for the same price ages ago. It's not even that great; it has a weird narrowing on the right side under the analog pad that makes the system asymmetric and uncomfortable.
They will be sold separately. Release dates (of either version) haven't been announced but it's assumed they are simultaneous.
I would not be surprised if the Vita version is download-only in the US.