Collection detail page is already the most useful thing on the site. Shows every file in a collection -- status, artifacts produced, errors. Grouped by source file, which turned out to matter more than I expected. When an ingest fails you want to see which source file caused it, not scroll through a flat list of artifacts hunting for the bad one.
This page is where I spend most of my time now when debugging. Not the logs. Not the coordinator's JSON endpoints. The HTML page I built a week ago.