A controllable LED riding in the edge of a Letus Extreme groundglass carrier, lighting the groundglass from the inside might not be so impossible but the edges of the screen might have to be dressed as well as being cut, to avoid internal reflections.

Think of it as a set in miniature. :-) How do you light a huge area evenly when you've only got one harsh sealed beam light, and space is limited? Maybe you could bounce it?

Just had a thought: if the camera itself is limited to 5.6, that rules out shooting in the street at night? I should have realised that all the DoF stuff I've seen has been shot in brightly lit situations. :-(