No, looking for a standard message bus that works across applications.
I don't mind that "each dbus-speaking application can define arbitrary methods with arbitrary signatures and arbitrary side-effects", as that's the whole point.
If you don't know the API the application uses, you can't speak with it anyway. D-bus or not. If you want to talk to an entirely separate application, use a header for that application with its IPC/RPC functions defined in it. That's the same thing you'd do with or without D-bus.
All D-bus gets you is an official version of the header I spoke of. Along with so much overhead that you can't use it for any kind of media streaming, apparently. And now they want kdbus; and I definitely don't want their code in my BSD kernel.
I don't mind that "each dbus-speaking application can define arbitrary methods with arbitrary signatures and arbitrary side-effects", as that's the whole point.