I’ve had considerably more time using Whonix KDE but for the better part of a week I’ve been on Whonix XFCE (using my same headless KDE Gateway) and have had zero issues with macOS and Manjaro hosts. At home I have a powerful i7 machine with 64GB RAM and the performance difference is negligible but at work on i3/4GB the difference is noticeable.
I suspect the vast majority of users wont dislike the change and the handful of KDE fanatics won’t be numerous enough to justify the effort involved to maintain a KDE version. I am biased though, since I started using Whonix I wondered to myself why KDE was chosen over a lighter weight environment when it is designed to be a VM.
Kudos on a job well done XFCE team.