I understand now. Yes that would work. That would put all your steppers on the same block. All the wires from the same point would be nice. More chance of getting cuttings between the belts and pulleys and that is all bad. 1/2 the current designs power, if you are trying to over come this with bigger steppers, they get big fast. and yes also more mass to move. Right now the x axis moves itself and the Z. Your way X and Y would have to move the mass of all three motors.
I am happy with what I made. I am not really sure if what you mean by all this. Scale it up for what purpose, more cutting power, more cutting speed, bigger spindle, physically bigger cutting area? All of those have different geometry. I made what I thought would be the best all around multipurpose machine that would be cheap enough to get your feet wet with CNC, and not be too limiting. If you have specialized needs, you might need a specialized machine.
One size does not fit all, in this case.