Would anybody be interested in a web directory that only consisted of other directories AND listed the pagerank of each?
Wouldn't that be exactly what this is? http://directory.google.com/Top/Computers/Internet/Searching/Directories/
There are quite a few directories of directories: AllWebDirectories andlinks Subject Directories Directory Archives Directory Pages Directory Search DMOZ: Reference: Directories Internet Search Engine Database Spherica Strongest Links Directory List
This is not a new idea and there are many possibilities out there to use. Are you thinking of creating a new one from scratch?