Considering the Enterprise usecases for JIRA, more and more customers are having huge number of Custom Fields and administering them on a single page is real pain and it takes lot of time to load it as well. In order to make this easier, it should be possible to search for custom fields in the administration screen (View Custom Fields). Also while loading it can just load the initial 10-20 fields and remaining can handled the same way Issue Navigator handles issues (multiple pages)