The early days when I was using iris, it had a nostr band incorporated and search was a great feature to read abt new topics talked abt on nostr but eventually it got too slow. Now I only head to nostr.band as a separate entity when I need to look back for my old book reviews. A flexible search approach is a good way to look for topics, like minded people etc. If the backend database is agile, it would also be able to customize trending topics based on relays and if relays can be split between personal, private and public, then it can cater to country-based or interest-based trending topics etc. Search on twitter is something I use when I want to have direct perspectives of what the domain-interest folks share about that specific topic. Many things can be expanded from search function but mostly it can be a tool to find like minded folks and content broadcast based on individual interest.