I think there's a lot more announced from Japanese third-parties already than for the PS4 at the time. PS4 didn't really get Japanese support until after a year (early 2015). Although the efforts so far for Switch are low (late ports and such), at least they're releasing games. The console market has shrunk a lot since 2011, so I don't think less enthusiasm is a Switch-specific thing. Most devs were still developing for the PS4/Vita combo, and will take Switch into consideration for new projects, which are then likely Spring 2018 titles (or later). The same happened with the PS4, except that console didn't have the first-party support that appeals to the Japanese audience.
My guess is a brand-new title, releasing for both PS4 and Switch. I will be disappointed if it turns out to be a smaller game like the ones we've seen on Vita and 3DS (aside from Tales of the Abyss ofc). I think it's been too long since the original release of Berseria for a port.
