The problem is that Rance 10 is to video games what War and Peace is to novels. The game is long. Very long. In terms of the amount of dialogue it's probably the longest video game ever made because there's a comical number of branching paths. It's less that Manga Gamer is being slow and more that the thing's long.
I fully expect they'll do it so that Rance 4 isn't a goofy hang nail in terms of dated visuals and not supporting anything resembling a modern display. But at the same time TADA's enjoying his retirement so I half expect it to be a sort of 'break in case of emergency' they're holding back.