RFC: kstart: Drop support for _KDE_NET_WM_TEMPORARY_RULES
_KDE_NET_WM_TEMPORARY_RULES will be dropped in kwin.
see also kwin!3501 (merged)
RFC: kstart: Remove support for specifying custom properties
While specifying properties in kstart is a powerful feature, it's also an obscure feature. Most users are probably not even aware of it (I, as a dev, discovered it only after digging through some kwin code).
In its current state, it depends a bit on X11. Making it work on Wayland is doable, but I don't think it's worth the effort simply because of how much this feature is niche.
Edited by Vlad Zahorodnii