I am needing to build one of these myself for a small lathe project. This is very cool. Great job on this. Fine details as well.
I have been just considering a standard rotary table myself with a snapping spring mechanism or catch release. It would turn all day in one direction without locking, but turn the other way and it would catch on the first tool location and be held mechanically by the catch and the pressure of the motor and gearing to keep it in place.
I just don't want to deal with the air system.