I would like to create some custom fields with large numbers of options. It is likely these fields will be of the "Select List (single choice)" and "Select List (multiple choices)" variety.
Given the large number of options I'd like to help my users out by presenting them with a search box rather than a long, long list of options. Something akin to the way that the user picker works when setting the assignee of an issue.
It looks like I'm in need of "Autocomplete and select list renderers" as described in Configuring Renderers, but these cannot be set-up for custom fields.