If you could create a petzval that worked for 4x5 AND had a shutter, this would be of much more interest to me sadly.

Actually, the Mamiya RZ's lens shutter works independently from the other electronics, it's possible you could set a simple function to simply trip the mirror lock up, and leave the rest of the functions to the lens as normal, if it had it's own shutter.

(And the Hassleblad C's as well)