Full text search has been merged in #Mastodon main branch, and will be in the next (and final?) 4.2.0 beta 🎉 It is opt-in, so it will take some time to be filled with people content as they enable their profile to be indexed, but this was one of the most wanted Mastodon features for some time. We plan to deploy it to mastodon.social and mastodon.online in the coming days to have a bit more feedback on it and see how it behaves in the wild.
Most people seem to not want to be discoverable with the exception of artists and other people who want to make money, I doubt search will replace hashtags as the primary discovery method