Another Idea. Builders' ability to remove trees/rocks when in base edit mode.
The title sums it up. Often (when I have just upgraded my town hall and have more walls and buildings), my creativity in how I design my base is hampered by pesky trees or rocks! It's not initially a problem, as the core of my map is cleared out, but sometimes I will build structures in a certain direction and the trees will get in the way. The inability for me to save a base in progress (which is another feature that they should add), makes this annoying as I am not about to go and flush the base in progress down the toilet to get rid of that tree. Of course you could only use this function when you have a free builder!
EDIT: Blast, it has already been thought of!