"no framerate drops are allowed... ever!" is a pretty harsh requirement. these games also need to render 2 unique images (one for each eye)
on the Vive, when the framerate drops below 90, it drops the framerate to 45, and reprojection kicks in. this usually causes some noticeable ghosting. you can turn reprojection off, but then if the framerate drops shyt gets stuttery, and possibly nauseating
most of the leaks about the Neo have mentioned it helping with VR. my guess is games will aim for that 60fps with 120fps reprojection for the PS4, while the Neo versions will actually hit 90 or 120 fps