I'm gonna agree and disagree with others here. Yes, the technical merits of a true monochrome sensor does make it a unique and better-suited way to shoot B&W. I'd love to be able to spring for a monochrom M or X camera for the same reasons I prefer B&W film as well - the ability to use colored filters to control contrast and tonal response. Yeah, I know you can do similar things with color files in post, but it just isn't the same.
But, as others have said, the economic argument against a monochrom sensor are compelling. Fuji X Cameras are a niche item for Fuji as a company, and from what I remember seeing somewhere vis a vis Fuji's 2016 earnings, Fuji's Imaging division only accounts for about 14% of it's overall revenue, with X cameras accounting for a mere 4% or so of that small percentage. I think even Instax sales account for more profit than the X cameras do.
Fuji has made it a point to keep its cameras and lenses VERY affordable considering the overall IQ and performance you get, and I can't see them developing a high-cost, low sales volume product for a segment of their business that accounts for such a small percentage of their revenue stream. After all, we do want them to stay in business.