I agree, you can use different size rims and ultimately get the same overall diameter (height) with tire size.
I think I read something about this here before but, I always appreciated the fact that the factory 17" wheels on my 1994 Impala SS were the same offset rims and same tires all the way around in order to easily rotate tires. It bugged me that my friend's Camaro had the same tires all around but different offset rims so you had to have them all broken down and re-mounted to rotate. The concepts both look fantastic as they are but I wouldn't mind if the could use the same set-up on all four corners.
Just me?
Ken