Hashtags didn't start out as a software feature on Twitter.
@chrismessina proposed their use, and for a long time, they were just a cultural norm.
It was months later that Twitter engineers turned them into links that went to a search result screen.
Same thing with @-addressing. It was a practice for blog comments that came over to Twitter, but there was a long time that there were no affordances in the UI to support them.
Same with retweets. People starting using "RT", and it took off.
You and I and everyone here are part of the first 10 million people on the fediverse.
We are setting the cultural and technical norms for the next few decades.
So if there's something you wish Mastodon did, or ActivityPub did, just start acting like it already exists.
If enough people want it or need it, it will get added by the software and protocols later.