The 2.x is basically a 2 axis design with a manual Z axis. All of the Z axis belts and pulleys the there, you just turn it by hand rather than do it through a motor. The front right lead screw is a little taller and has a 1/4-20 nut on the end. I use a nut driver on it, but you could use a detachable spinner knob with a little design effort. You rarely move the Z axis very far so it is not a big deal.
I did this to keep the basic cost down of the machine. Everyone complains about the cost, but once they start building they decide to gold plate everything and order every option. With that in mind there was always a plan for a motorized Z option. Here is a rendering of what it looks like. I have all the parts, but have not had the time to install it yet. This would be compatible with a stepper or gear motor. The gear motor should be in the 100-200 rpm range for decent performance. The stepper motor version would be geared down (as shown) for extra torque. This mounts right where the existing left rear lead screw goes.