Do you mean searching your own conversations or search all of them?
Discussion
I started building a broader user search on https://sps.bio. Always happy for feedback.
Searching for things in general. Like if I wanted to find news or topics on Twitter. That might be a problem for a decentralized system where you only see a small portion of the total data.
Search/indexing can be centralized at many places though. Big search players will probably come in at some point in time.