No more delays expected, May 25th for the JP release. Set to release in the West this fall through NISA, alongside a PC version for that western release. Development complete. 1080p 60fps.
Ys 8 PS4 has new music and new content that wasn't in the original Vita version. It's assumed the PC version will be based on the PS4 version. It also has a new difficulty setting, Inferno.
A short bit of footage from one of the new Dana areas (made a thread here: http://www.neogaf.com/forum/showthread.php?t=1360017) as they acknowledged the Dana parts of Ys 8 needed more fleshing out so more content was added.
As reference - Tokyo Xanadu ex+, the PS4 version of Tokyo Xanadu from Vita also from Falcom, had an entire CD's worth of new music and quite a bit of new content including more chapters, new playable characters and new bosses. We'll see just how much stuff got added to Ys 8 once it comes out.
If you want to get a feel of the game, the Ys 8 PS4 demo is available free to download on Japanese PSN so you can play it in 1080p60 for yourself.