It probably actually is a quick initial implementation, but like everything else, it needs to be planned, ticketed, developed, tested, and slated for release.

Compositor work isn't tremendously hard when the graphics primitives are already done.

UI state handling and input is a majority of the work from there. I've implemented this work before. A large portion of my background is in compositors and UI primitives.

What's really cool about having window backing layer handles, is you can do all sorts of crazy fun stuff in the office and show off to your coworkers or tech demo that basically will never make it to production because it's totally impractical.

The best example of that which actually did end up in a final product in my opinion was Windows Flip 3D. Totally fun implementation, I'm sure.