Along these lines, I concur on matching the 6.25” form factor.  My Dynon com looks a bit out of place between a PS audio panel and a Avidyne GPS, but made it work.  
Solution: offer the various control heads in a 3” wide by 1.5-2” rectangular form factor with a one or two hole Dynon front plate.  That way, builders (or certified retrofits like me) could include one or two control heads seamlessly in their audio stacks.