Blog categories and directory

Some of my users have requested a feature I had thought about: a blog directory. But not like the list-all blogs plugin thats out there, I'd like to have the ability to let users select a category, and then display a directory with all the current categories and all the blogs in there. Plus, a link to the blog, a short description, the screenshot of the theme its using and the ability to rank said blog.

Since I host blogs of all kinds, this would be usefull for people to find blogs with topics they are interested in (the tags help, but its not the same).

How feasable would this be? I'd even pay for it as a custom plugin (depending on the price ).