The kdbuswreck

The "starting point" would be a file descriptor inherited from the parent process. Today we have "standard input", "standard output", and "standard error"; now imagine adding "standard desktop" which is a socket that implements some protocol to talk to the desktop session.

This file descriptor would support a bunch of standard functionality that all apps need (like, opening windows, or raising notifications, etc., but NOT things where the user might want to choose the resource used or deny it for security reasons, like printers or audio devices or connected OAuth accounts). It would also have a way to say "I need an object (file descriptor) implementing protocol X", and that's when the user is prompted to choose which object to use. Once the user chooses something, the app can save a long-term token representing that choice and re-request the same object later using that token.

Yes, this is "standard desktop" FD is similar to the dbus session bus, except that I can decide which programs that I run are allowed to access it, and I can mock it out, audit usage, sandbox, etc., as described previously, and I can make choices about individual resources accessed by any app.