The current lists/members API returns the members of a list paginated to 20 user records at a time.
For a full-sized list (with the maximum of 500 members) this means it takes 25 API calls to return all of the members. Even worse, this API is rate limited - and just pulling in the members of a list will burn through 25 queries very quickly.
The friends/ids API returns a list of the numeric Twitter IDs for the users that someone is following, 5000 at a time. It's really powerful, and is a key API for several projects I have built which would not have been possible otherwise.
Having an equivalent API for bulk-fetching the IDs of all list members would elevate list membership to the same level of power as following in terms of the Twitter API, and enable a whole bunch of interesting applications to be built that aren't really practical with the existing lists/members limitations.
Updates
- Acknowledging as a feature request. Thanks.