I am in favor of saving the package-selected-packages to a separate file
and would also volunteer to make that change.

It's for these reasons I do not find that variable being saved in
custom-file very useful:
- Sharing the custom-file across machines
- diff of that change is difficult to read as all package names are in one
line. So I always blindly commit the change to that variable as I know that
it will be auto updated by emacs when I install/delete the next package.

Saving this variable to a separate file makes sense to me because:
- This does not need to be git controlled ( I can easily gitignore this
file ).
- All my machines using emacs can have their unique
package-selected-packages file (for example: I don't install all work
related packages on my home machine).