@ifixcoinops@retro.social @ireneista@adhd.irenes.space An alternative to the subject line might be categories. I don't think I'll ever stop going back to Google+ as the best example of social media until somebody finally makes something better.
Late in its life, Google+ added a feature that I don't remember the exact name of, but I think it was categories. When making a post you could select which categories to tag the post with. This was made separate from hashtags in the UI. I think this was the brilliant piece. Although functionally there was little difference, hashtags are such a poor experience if you're not well versed in the practice or deep in the community they relate to.
Anyways, when you made a post with a category, any of your followers could select which categories they were actually interested in seeing. So if they wanted to see more "hole" but didn't care about "shaft", they selected only the one category to see.
I think the goal is to create a filtering/discoverability tool. The mechanism I'm suggesting is categorization. My preference for categorization is a good tagging scheme, but hashtags as they exist now are definitely not it. I expect that subjects are too free form to be a useful categorization system.
Or maybe categorization is too complicated. Nobody should have to be an amateur librarian to make a post.