I was talking scale-up in a general way. We should keep in mind that changing scale, usually, is not linear. At some point you need to make more changes than axis length. But i digress... scale up is not the point.
My point is how good (if any) would be a design with the (3) axis motors attached to the spindle support? Could it be faster by using bigger motors? Acceleration issues? Torsional/mass issues? Or, not even good enough to consider? :)