I haven’t been working on this yet, but this is pushing it up my agenda 
Just from a technical perspective, yes this should be possible.
Not yet. The next thing we’re adding are Tag actors (I’m working on this right now). These are the current and possible actors:
- Category actors (current)
- Tag actors (soon)
- Topic actors (later, if it makes sense)
- User actors (these already exist, you just can’t follow them; follow may be added if it makes sense)
Personally, I feel that just following a single topic may be a bit “granular”, particularly if tag actors exist. In other words the circumstances in which you want to just follow a single topic and not a tag, category or user seem pretty marginal to me. But let’s see.
There are a few examples in Fediverse Futures - SocialHub, you can see some “full topic” discussions (i.e. including replies), for example
Click on the post status icons to see more about the ActivityPub details of that post.
Also, @devnull and I are actively working on getting a link up and running between this forum and community.nodebb.org. Soon!