Plasma's login experience is an area that we know requires some improvement — it works OK in the basic case, but it's very barebones and doesn't handle anything beyond that.
This roadmap looks fantastic, especially the focus on moving away from monolithic, easily-broken QML themes in favor of tighter integration with Plasma’s native settings.
I had an idea regarding the “Customization” aspect you mentioned: Since the new architecture aims to use existing Plasma theme and color settings, would it be possible to have the login manager dynamically switch its theme/wallpaper based on the selected user?
Essentially, when you click on a user’s profile picture, the greeter could “preview” that user’s specific desktop theme and wallpaper. This would:
Give the login experience a very personalized feel.
Directly leverage the “syncing” of native settings you described.
Provide a visual confirmation of which user is currently selected before entering a password.
It seems like this would fit well with the goal of bringing the design in line with the screenlocker while making the most of Plasma’s existing configuration engine.