In this thread https://old.reddit.com/r/visualnovels/comments/a2otxh/jast_holds_the_rights_for_two_classic_games/ here one "jsmile" makes a post representing themselves as working for Jast and saying that Muramasa is being worked on. Now, to my knowledge, Muramasa has never been announced. I very much doubt you would announce such a thing in a Reddit comment thread (besides which, the account's other posts aren't consistent with an official account used by anybody).
(If you're wondering, it's buried in the hidden-by-default thread started by Gurthangistan at the bottom)