If you got the skills and equipment it's not that difficult to do a middle case.
I beleive most cases are punched in several casts before the milling though. But it should be possible to mill a case from a solid metal piece aswell.
The simplicity of the sub, yet so difficult to rep for the manufacturers. How hard can it be?
I think seans case is too expensive.
To much work and $ to make it perfect.
IMO the biggest challenge building the perfect sub is the ss bezel and bracelet/SEL. Gen is the only alternative at the moment.
The rest can be fixed quite easily on both the wm9 and etaswiss.