Builders seem pretty pointless and just clogs the screen. At least one other person has thought the same. So instead, if possible, move the improvement action to the city screen instead. Actually makes lot of sense when you do all tile management in that screen anyway. Including districts, tile buying, citizen assignment. Only thing left is improvement. Unlike the former workers that stuck around, since builders disappear eventually, really pointless to turn them into units that clog up the already cluttered 1UPT map. If this is possible, the mechanic will have to be rethought from the ground up. i.e. the cost, the interface, the civ and leader ability, and AI handling.