It is a desktop file. Really the memory savings would be valuable outside of Qubes too though, so I implemented a small service in usability-misc that just moves the desktop file out of the way on boot if the system is booted in a mode where it’s not needed. I’m realizing as I type this that the mechanism for moving the file back should be made slightly more robust, but that’s a solution that will work everywhere.
I just moved it to a different metapackage, so it shouldn’t even be installed on Qubes anymore.
I did implement a lot of the other solutions too, or at least started work on implementing them. The polkit agent solution will only work in a limited number of scenarios, and smart-notifier was an entirely new addition that just wasn’t expected to take up so much memory. We were having memory usage issues before that, so hopefully this will get RAM usage actually lower than last time we were using too much RAM.