I can’t really find any information on where one would submit a feature request for KDE products – it seems wrong, to me, to submit them to the bugtracker.
I found this Reddit thread that seems to say that there isn’t one, but that post is, as of writing this, 6 years old, so I’m wondering if anything has changed since then?
The ‘Help → About KDE → Report Bugs or Wishes’ dialog available in most KDE applications ends with this paragraph:
If you have a suggestion for improvement then you are welcome to use the bug tracking system to register your wish. Make sure you use the severity called “Wishlist”.