A lightweight version of plasmashell is being developed by KDE:
It is far enough now that it can be tested. It runs fine, let's you use your desktop without issues.
After installing, run it manually by stopping plasmashell and starting it:
kquitapp5 plasmashell && liquidshell
When you want to get back to regular plasma (on reboot you will have it, nothing changes on your install)
kquitapp5 liquidshell && plasmashell