I think you fail to appreciate what a good CNC system can do. The same system that can crank out 1 mil accurate cases can also do mainplates, bridges, rotors etc.
The only reason they don't is the easy availability of off the shelf movements.
Custom movements might raise the cost of super reps a few hundred dollars, but if there's a demand the current technology can supply the goods.
Then again, if it's a closed back case there's really little need for a rep movement - look at all the reps running a 2824 clone where the gen never had an ETA in it -