WYSIWYG: The suggestion is the ability to merge buildings.

Example of when this is useful: in the Spiffinmoore level, I wanted to take the starting two buildings and the 3rd building on the adjacent lot and create a large ring with a courtyard in the middle. Without building merge, I ended up having to delete entire buildings so I could expand a single building into that same space.

Yeah I had to do something similar.  Not being able to merge buildings on different plots I can kinda understand but on the same plot it made no sense to me to have to delete 1.