> Pretty neat way to get a "2 speed" transmission.

It's almost identical to how the two speed "transmission" works on 12 volt Power Wheels toy ride-on vehicles.

In those, there are two motors connected to the rear wheels; one for each wheel. Using a couple of switches on the "shifter", the motors can be connected to the battery in series (high speed) or parallel (low speed).

Also interesting is that by using two separate motors in that manner, you gain a form of "electromechanical" differential (not that it matters much, as the plastic wheels have insane amount of slippage on most surfaces).