Hey @Petr_Mišák,
To do that you’d need to have comments created on Wordpress be imported as posts into Discourse. That’s not possible using the WP Discourse plugin and unlikely to be supported in the near future. For some broader thoughts on this see
That said, it occurs to me that once we add the ability for Discourse category actors to follow other ActivityPub actors to the ActivityPub plugin (which I’m currently working on) you could perhaps configure the Wordpress ActivityPub plugin in some way to achieve this. Although this is quite speculative.
I’d also want to understand a bit more why you see this as “resource intensive”. If you’re publishing a lot of articles that aren’t getting engagement, perhaps consider publishing a subset of your articles to your forum that are more likely to get engagement? Conversely is having a lot of embedded topics with no replies hurting your community in some way you’ve observed? Is there perhaps something you can do to address the underlying issue here so to speak?