Ultimately, I think that Troy and Co. have to figure out where they would like to see this project go.
If CtC is mostly limited to a study of picking technique, I think you’re correct in that there’s a natural limit to what can be covered. There are only so many ways to move a pick quickly and efficiently.
But if the goal is to study virtuosity in general, then there’s a lot more to potentially study. Left-hand technique, for example, hasn’t been looked at very thoroughly. Someone like Holdworth would have been a terrific case study – his left hand technique is notoriously difficult to replicate, and shrouded in the same sort of mystery and confusion that characterized picking technique for a very long time.
Then there’s the even more elusive “though process” – how certain musicians are conceptualizing what they play. It’d be particularly enlightening for jazz musicians and other improvisors, since they’re doing most of their playing on the spot.
But that’s all a ton of work, and frankly Troy has put more than enough time and energy into this project already. If he decides to limit it to mostly picking technique, I certainly wouldn’t fault him.