The latest commits I've pushed was me polishing the QML interface, mostly. The most difficult part was getting the authentication to work properly, but that works now. It still needs some improvement, but I recently got the embedding working (the migration to QML made it regress), so e.g. the unlock widgets dialog, which requires root access – works.
The nice thing about using Plasma, besides allowing widgets on screen (as well as simple things like a keyboard, clock, etc.) is that it enables retrieval of otherwise inaccessible data – like weather, for example, which is just ridiculously impossible to access otherwise. So if somebody wants to make a "theme" for kdm-plasma, to respond depending on what the weather is currently like, that is certainly possible.