My opinion is that this instance is too small for it to be worth it. We already have other communities and they are very inactive. The Krita and LabPlot communities barely see any activity and they're some of KDE's biggest applications. The KDE Edu and Akademy communities are even deader. Even by combining everything else into one community this instance isn't exactly busting with activity, so best not divide things further. It's already seeing fierce competition from the more official KDE Discuss (and the Krita Discuss) and the more popular KDE subreddit (and the Kdenlive and Krita subreddits).
Yeah, it'd be great to have developers participating in discussions on here, but I don't think most would have either the skillset or desire to moderate a community. Obviously there would be some exceptions there, but I can't see a reason as to why it would be mandatory.
When your too busy moderating the community to contribute to kde, so you lose your moderator status. You're also too busy contributing to kde to moderate the community.
It might be good to post about those topics in this main instance, even if those communities were made (cross posting to both). Otherwise people may not see the posts
I think for now the userbase is too small and this would be unnecessary or even undesirable. As it is, there aren't all that many comments on posts in this community. Down the road it certainly wouldn't be a bad idea though, especially for the packages that people who don't use the DE may use.