Scale up a few of the mini golf maps and change them a little so that they are challenging enough for ball race. I think it would be cool to experience the familiar maps from a different angle 
what would be even cooler is if you can use ball race/minigolf background sets as prefabs for the SDK or something
if they have to get earned using units than fine, I guess.
Heck even older versions of the background like the OG background of ballrace midori.
Like wouldnt it be cool to be able to edit in the world of Ballrace event horizon with the option to move/disable the big stars and black hole in the background?