GujjuGang7 on Reddit found this, saying:
Found this link while looking through the upcoming theming engine (Union) repository. It has mockups for several core apps (dolphin, Kate, konsole and more) and general components such as modals and titlebars.
KDE contributor Manueljlin would like to remind you:
hey folks, it’s really early still. we didn’t even properly show it at Akademy. there’s no design system to properly back it up yet - only some tokens and components that are definitely subject to change. please keep that in mind
There are some really nice designs here. I really hope that KDE finally gets to pay attention to this. I love simplification of it.
One thing I don’t like here is the login screen. There is too much stuff on it. I think gnome’s login screen, as it is now, is fantastic.
And one more thing, proposal for mindset change: not everything has to be a widget. Some things (like shell) could have layouts: layout as current plasma/windows, layout as gnome, layout as Mac, layout as Win8… If things get well thought out, you can integrate this and switch layouts and not di*k around with widgets. Less moving parts, less problems.