But they don't take more time to move (on the same partition). Also it would be nice to see at a glance if a folder contains a lot of data (number of bytes, not files) before starting an operation.

if you are moving a folder of files within a partition (hey, this was your idea) then you don't care how many or how big they are. only if you move them to a different partition would you care, but in that case as you hover over the other partition, you'd want the folder to become helium or hydrogen light, so you would need to exert more force to get it to touch down in the folder. oh the humanity!