I think I'd like to do this, not sure what I'll do since I've already got a Cromwell (my favorite British tank) in progress but there is a wide selection of interesting things to build. I've had my eyes on a Bishop for awhile but as Sept is some way off I want to shop around.
Just a comment on the commonwealth designed and used, there are a number of vehicles that were not fully designed by but were only used by commonweath countries the Chevrolet 3 ton was built in Canada and only used by the commonweath countries but is an American designed truck, Grant was a modified version of the M3 medium designed by and for the British, it was not used by the US, Staghound, Boarhound (I'd love to find a kit of that) were US designs contracted by the British, Firefly is based on the US Sherman as is the Canadian Ram, and Sexton these were strictly commonwealth vehicles but based on a US design.
I realize you are trying to get away from Sherman's in commonweath colors but a number of commonweath vehicles are being excluded due to their association with the US base vehicle. but there seems to be a blurry line with a few cross overs being allowed (Chevrolet 30 CWT, Sexton) and some not (Firefly, Grant, Stuart Recce). I'm in regardless as I will be building something wholly British, unless a cheap Boarhound shows up
but there are a number of vehicles that you don't see much that meet the criteria except for their US roots.