Microsoft Trackball Explorer XX made by Massdrop
I can't use a mouse due to significant RSI injuries. I use a 15 year old Microsoft Trackball Explorer and whilst I am fortunate enough to have a couple of spares, no one has ever come close to making a trackball that is as comfortable to use. Trust me, I've tried them all.
They have a cult following and new ones sell for $600 on Amazon. Microsoft has shown no interest in returning to the marketplace but I wonder if your biz dev people could convince them to let you make a Massdrop made version.
Judging by the prices of these Fabergé eggs of the pointing device world I imagine there is a significant market for these and I would be first in line to buy one, two or ten.