Wiping out a race is fairly tedious. Which made me think adding a single unit to the game to make it easier/funner to do it, would be good. Then I saw Kaiju-A-GoGo (e.g.,
https://youtu.be/dJBULxOdli8). Which lead me to:
SBR should allow the building of a Kaiju. It would function as a moveable building, that has a short range attack. Each turn you could move(rebuild it, with the same health) it in an adjacent space. It would also offer attacks. It would be killed just like a building. This does break the "no-units rule", but I think it would be fun.
PS I also really think the game needs more Dinosaurs and Giant Robots.