First, the way the site indexed doesn't really lend itself to a search feature, since there's not individual pages for the sheets, so there's not really anything to easily index.
As for the 2nd, browse by composer is wayyyy harder than it sounds, because the composer isn't in plaintext in the file so it's easily indexable, and a large number of composers, particularly those on older sheets, are named incorrectly or inconsistently.
They are things we, as a staff, have considered, but they are not things that will be implemented soon. As for a community wiki, there's not a real reason when VGMDB does it better and has a better database already.