There are plenty of tank lines they could introduce to the game that would be fun additions without needing a gimmick. I think people would play tanks that were cosmetically weird or cool, were similar to things they already liked but a bit different so they have more flavors to pick, or just added more vehicles to a nation they're interested in playing. Swiss heavies would look cool, Swiss mediums would be a new flavor of NATO style medium, they could add more British vehicles easily, or add Japanese tank destroyers, or add a branch of single shot Italian medium Patton clones even.
(Als