Are you planning to offer general factory services at some point in the future? Things such as: soldering wires to PCBs, screwing PCBs to 3D-Printed enclosures etc.? I think a service where you offer workers at an hourly rate on workstations with basic tools (screwdrivers, wire strippers, soldering iron) would be amazing. Especially for medium volume projects (say 1000-10k units), where assembly in china would be great, but sourcing factory yourself can be a complicated process. I would imagine the flow something like that you can order a "test round" where an upper limit of time needed per assembled piece is determined with 2 or 5pcs (pre-paid of course), and afterwards you can just order this exact assembly service for whatever quantity needed. Lead time estimation should be very simple with this method. JLCPCB is already disrupting PCB and 3D-Printing services - if you can manage end assembly aswell you will be unbeatable.