The current setup already shows if there are additional comments:
…I don’t have a problem with that. (it encourages readers to use our discourse forums) I hope that never gets replaced with what you are mentioning.
I didn’t mention the WP-Discourse plugin in OP because I’m happy with it as it stands.
I really prefer to keep encouraging any discussions to take place within Discourse. What you suggest isn’t only more complex but also removes some of the need/habit of visiting the forums.
Also, my blog has a lot of caching enabled, so there’s that as well.