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.
Aren’t searchability and discoverability two different things? I understood hashtags as a way to make your post discoverable, or more accurately, to comment on a topic that there’s a consensus term for and so everyone can see your opinion. If I was looking for a specific opinion, some piece of news that I remembered a short sentence from, then I would search for the phrase I remember.