I love the concept and it seems like there was a lot of thought put into it.
However, with Cherry MX switches in the new design, I'm seeing one heavy pointing device. Even with PTFE (Teflon) skates and a low-friction mouse pad (hell, let's use a PTFE mousepad), that's a lot of inertia. I can't imagine that it'll be easy to point accurately with this. Then again, if they can keep the weight of each unit under, say, 180 grams (what I'd consider the absolute maximum weight, including battery, for a mouse), well... is that possible with PCB mounted Cherry MX switches?
Now a commercially available mechanical split keyboard with a 50mm class trackball, like that amazing DIY one I read a build log of here, that I would buy. And no need to worry about weight with those. But I can see why the developers didn't go that direction- there's not much market for trackballs since mice went optical.
I just can't help thinking that this might be one of the few places where you'd actually want RD+Membrane or Cherry ML switches.