I have the same problem. Our forum's photo gallery has about 1000 categories.
When attempting a media search one is confronted with a huge long list of categories.
Actually they are structured in a nested logical tree structure, but the search box shows all levels.
The enclosed screen grab illustrates the problem. It shows top level and three levels below in this first tiny snap on the whole list.
Is it possible to display only top level or maybe top and second level initially, and then open up sub categories by clicking in the list?
Any tips very much appreciated!