I want more "stops", similar to the two on the tool.   I want to build a tool similar to this where the domino is mounted on a "table".  I finally figured out that if I wanted additional "stops", I could put dowel pin inserts recessed into the table.  Put the pin where you want the stop, remove when you don't.   Clearly, yours is much more flexible.   However, I find that with dominos, they don't need to be super precise (like you would with a saw's stop), but they do need to be consistent.

Pins in the table means you have to center the Domino to the pins (left/right pins) when you mount it to the table. Could of course be done but might be trickier than it sounds. No the pins doesn't need to be super precise when it comes to location but they need to be very precise in terms of equal distance to the center of the cut on left and right side.