Grouping by interface type or implementation language is less useful than grouping by what things do for the user. Small categories are generally more useful than large ones We lean towards lots of little categories rather than a few big ones. This makes individual directory pages easier to digest. If the directory structure is well designed, it also cuts the total number of package descriptions a user has to sift to find the right thing. In general, if a directory has subdirectories in it, it should be all or nearly all directories.
Subdirectories are hard to spot in a thicket of package files.
How maintainers become maintainers. The MetaLab archive is maintained on an entirely volunteer basis by a small group of senior Linux hackers. If you're qualified, you'll be able to figure out for yourself who to approach about joining the group, and how to approach them. We don't need to see a resume, but it would be helpful if you could point us at a successful Linux FAQ or freeware resource you have maintained. For packages that are updates of stuff already in the archives, this is a semi-mechanical process.