True or not the Onimusha series is one of those series that doesn't need a reboot and if anything just needs a proper sequel. Between the 4 there was 1 and 3 which actually followed the main Character Samanosuke Akechi and are easily the best in the series. Then there was the 2nd which was more or less a filler and wasn't at all bad. The 4th on the other hand was just a joke because it wasn't at all like the original 3 and I have no idea why they'd even considering this over the original formula.
Point being I love the Onimusha series and I always wanted another proper sequel. They could easily pop out another game with Samanosuke Akechi or a game featuring Kaede (his side kick from the first game) who we all know dies eventually while searching for Samanosuke so that alone would be interesting. Or they could make another game like the second which has a completely new cast and a ton of new features that wasn't used in any other game.
The series is still fresh and the ideas are endless so a reboot is probably the dumbest thing they could do. Now a sequel? well.. a sequel is the smartest thing they could do.