While it probably would help people on Mastodon find content in some circumstances I’m not sure it is necessarily a good idea. They can already follow sublemmies, communities so that is an organising principle. It might be a case of trying to do too much and confusing people. Exactly what conventions will be used by people posting from Mastodon into the lemmyverse and vice versa are not yet clear so maybe deliberately using conventions from one platform on the other will develop. Will be interesting to see how things play out.

By the way when viewed on Mastodon this hashtag is clickable unlike some hyperlinks posted from lemmy; it is not showing up in search though(on https://masto.ai)

Unfortunately there has been a wave of fake accounts being created on lemmy. Requiring email on signup is one way to try to prevent this from happening.