I haven't sold any from a flatbed scanner, and gave up on those a long time ago. But I do sell images from time to time, and the RB67 is my main camera. I scan on an old imacon scanner that brings out resolution a dSLR can only dream of. I usually have to downscale the images.
A good photo is a good photo regardless of medium. Medium format has a look that is hard to emulate. You don't really need a niche IMHO, just have a clear idea of what you want to convey with your images and work as hard as possible to achieve it. Stay true to your ideas.