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.
Brand new interactions and interfaces. 
Easy to use and quick to get started. 
Hello and thank you for your suggestion,
We appreciate your comment regarding the integration of the 3D printing service with our PCB services. Currently, the 3D printing service is considered as a newly released feature, and we are still in the process of introducing some upgrades to enhance its functionality. While we acknowledge that associating the 3D printing service with PCB services could be a valuable feature, we are unable to implement it at this time. However, we will carefully consider your request for future enhancements.
We sincerely appreciate your feedback and thank you for your understanding.
Best regards.