If I ever went with the 13.6" screen size option, It's much more likely that I'd start with the M3 Max as the base machine instead of a custom approach. The LCD and light source seem to cost a considerable percentage of a single M3 Max.

On the other end of the spectrum, the 6" 4K Photon Mono 4K can be purchased for £145 shipped at the time of writing. It also uses Anycubic's slicer, implying that it doesn't require an SDK from Chitubox. However, after analysing what things I'd want to send to the printer, I can only really see this printer used for R+D purposes and parts/models that just happen to fit due to the limited build volume.

Anyway, it seems that a lot of the components needed for a VLM machine can already be found pre-bundled into a modern MSLA printer. This also simplifies the BOM greatly and should make it much easier to build the printer if designed. I'm not sure about the M3 Max, but I'd assume it'll be possible to 3D print a custom plastic enclosure for the Mono 4K if needed so that it better integrates with the VLM style machine.