This page tracks the Wayland showstoppers through out the stack
Session restoring does not include Wayland native windows. Our sessions management recover engine is based on the X Session Management Protocol and there is apparently currently no generic concept to do it on Wayland. But on Qt it's plugin-able and GNOME has according to their wiki an own implementation for some time.
KWin uses NetWM modes internally to do this. Works with Xwayland clients.
From Wayland to Xwayland ignores. From Xwayland to Wayland falls through.
We don't have an API yet for remote support. Even if we had things like TeamViewer would not work any more.
Partly fixed since we now have an API for screencast using a separate KWayland interface. There is also already support in xdg-desktop-portals for convenience of other apps and general support in Flatpaks. What's still missing is an API for remote input.
The NVIDIA blob is not supported as it uses a custom EGL extension. It would require additional code just for NVIDIA. On the other hand many users are on NVIDIA. Further information: To EGL Stream or Not and Plasma/Wayland and NVIDIA – 2017 edition
QT_QPA_PLATFORM is set to wayland breaking any application which has Qt included (e.g. appimages, proprietary software) and doesn't have wayland QPA.
Fixed by not setting the variable in system, but let every app decide on itself. With 5.11 setting this variable is not needed at all anymore, because it autodetects the windowing system.
KWin lacks integration the tablet support from libinput. Also KWayland lacks wrapping the API for it.
X has the ability to accept fake input events to allow programs such as Easystroke. With the new security model of Wayland, such a program would need to be part of the compositor.
We lack a functionality like XModmap to remap keys. See xkbcommon-issue40 --> Explain how this issue is related?
We don't have an API yet for virtual desktops, so pager is not working
We don't have an API yet for window thumbnails.
Broke with switch to XdgShellV6. Needs new API added to Qt (native interface), KWayland and Breeze.
Activities are probably not a must-have feature, but anyway this is annoying for those who got accustomed to them on X11.
Fixed in Qt 5.9.5
Fixed in Qt 5.11
QtWayland does not yet support the tablet API. So even if KWin had support Qt would not be able to use it.
Fixed in Qt 5.12