This is very clever, and details like these will really separate Marlin from Nautalis or other FMs. I don't know if this would clog things up but would it make sense to add how large the files your are moving are, either as a group or individually. The size of all the files together on the clipboard would be handy. I know it might help me if when searching around for files to put on a flashdrive, or dropbox etc.
I also wanted to add, that I think this is moving in the right direction in that it is taking what as always been a pretty ethereal process and making into a very tactile one. I really believe that touch screens and tablets and all that is direction technology is moving in. Shifting our UI metaphors into tactile ones like this will be much more comfortable than they are now and make Linux/Ubuntu/Elementary OS/whomever more desirable in this new market.