There has been a fair amount of discussion here about mouthpiece preferences, GhOstCOde, and some also about creation of 3D mouthpieces. Search the forums for “3d print” and “mouthpiece” and you should be able to dig it up.
Preferences among members are all over the map. I guess everyone agrees that a mouthpiece should be smooth and feel comfortable in the mouth or against the lips. And most will also agree that we need more options. This is especially true with the Yamahas. Suzuki has offered the most options, but they don’t fit other popular brands, Yamaha in particular.
I personally like short, minimalistic mouthpieces such as the Suzuki MP-142. Another favorite of mine is the melodica-end fitting from a Suzuki tube.
Some nicely crafted new options would be very popular, though it’s probably not a get-rich propositions. I hope you will pursue this vigorously!