We could implement "incremental search" in the web UI. Incremental search is a real-time search feature in which results matching a query are immediately rendered on the page. This is like how Helm and similar work on Emacs.
According to the above Wikipedia article, Google implemented incremental search under the name "Google Instant", but later discontinued the service. I wonder why.
For incremental search with Xapian, special considerations with the query parser apply.