they should be doing what is essentially a sequel to it, as well.
Using the same graphics engine != sequel. The games don't play anything alike, and in fact most of the previews I've seen for Muramasa say it's about as far from an RPG as you can get.
And Ignition is a publisher, they publish games regardless of where they came from. Most of their games have come from Japan, IIRC, but that doesn't mean they can't publish a US game.
I'm mostly scared about this because of the terrible job they did porting Lux-Pain. Their work on the manual for Metal Slug 7 doesn't have me in high hopes either.