While this may not be quite as well polished as the original version. I wrote a small console utility that does the same thing.

It is purely commandline based.
Setting the root directory is done using the option "-d" followed by the root directory to search from (example -d "c:/familyphotos")
Extension filtering is done by "-e" followed by the extensions you want to include (for example -e "wav,ogg,mp3")
The amount of files for you to choose from is set with the "-t" option followed by an integer.
This changes the behavior slightly if higher than 10, as 10 cannot be input in a single character. So when selecting you have to hit enter as well.

This gif should illustrate:

If no one else takes this, I'll take a shot at it in about a week.

Shouldn't be too horrible to do.

edit: Done diddly.

Pull any folder you want on to the executable and it will count the folders and files inside and rename the folder to "# OldFolderName". I put the sourcecode rar as well. If you want it for multiple folders at once that can be easily done.

Edit edit: Okay, added functionality to drop multiple folders in at once.

Requires .Net 4.6.1