Physint's the working title of an original IP Kojima Productions plans to do in the future. Kojima mentioned that it'll be inspired (also IMHO pay homage) to the Metal Gear franchise.
This was announced recently on early Feb. Sony's going to work with KP on this.
It'll be like DS in terms of assembling the cast/crew.
https://www.youtube.com/watch?v=8SegRMGH_K4&t=2790s (Latter link is the announcement of Physint in Japanese)
No further details on it yet (story, setting, characters, etc.)
Kojima-san says to stay tune.