I think it depends on the use cases for #MedMastodon. IMO communication among peers can be done by looking at the local timeline and ensuring peers outside the instance are being followed. Hashtags (on the other hand) are good for allowing folks across multiple instances to participate even if they follow noone. I think the size of the fediverse can make hashtags not good for ongoing discussions as thread of conversation become lost in folks "broadcasting".

While the algorithms of other social media platforms push users to see feeds that push them deeper in their own bubble, mastodon users are self-herding within servers that show local feeds (as one option). #MedTwitter existed across the entire platform. #MedMastodon is over 70% happening within med-mastodon.com

Community of interest or more segregated from other audiences?