Do hubs open up some new ways to think of a Farcast native hashtag?

Some blend of a subreddit & topic specific feed? 

have seen topics on here being mentioned under a subdomain style thing like topic.fc

It’s probably up to clients. Essentially “topics” I.e. any form of filtering information requires information. Hashtag, subdomain, whatever, as long as computers can read them. #topic is kinda perfect. #topic.sub works fine. Regardless, all this requires client support. Many novel options there!