Currently KWin is using OpenGL 3.1 for rendering (or 2.0 or Xrender optionally). It would be good to implement Vulkan renderer for many reasons. Not only Vulkan drivers have less bugs and more commonly provide more stable experience, but from the integration perspective, let's say when someone brings Plasma to a new hardware platform, it's easier to implement a Vulkan driver for it first, than OpenGL one which is a ton more work overall even for 3.1. This way, Plasma could be brought up sooner, due to having easier to create prerequisites. As an example, consider something like Librem 5 and such. Instead of working on OpenGL support there, Vulkan could be the first focus (smaller effort) and then something like Plasma Mobile could have been used there sooner. Either way, Vulkan is the modern GPU API, so it would be good to have it as an option for KWin, so I'm opening this to propose it and keep track as well.
There has been some work on a vulkan backend. https://cgit.kde.org/kwin.git/log/?h=fredrik/vulkan I am very skeptical of the deployment claims as until QtQuick's RHI lands you would need the GL support anyway. In any case, big tasks are not suitable for a bug tracker.