HowAmIBrous doesn't work with anything but D2. All of their blades are hand ground, they are not mass produced blades. Each one being made by Jason himself. I have a Brous T4 flipper that has been a great knife, although I have other blades that I use for utilitarian purposes. I'd never sell it, I love the action and the feel of the flip.
I don't really think Brous needs to add a ball bearing, the bearing system they use is very fast.