Compile Heart is readying not just a new Neptune game, but a new Neptune series!
Watch the mustache guy from the recent Compile Heart teaser site "summon" the new series:
At the end of the clip, he says "summon."
You may remember the mustache guy as a member of Microsoft's Xbox 360 Special Forces Division. This is probably not to be taken to mean that the new game(s) is(are) for Xbox 360, of course. However, Compile Heart has not announced platform details.