> Maybe simply the ability to spread the saved custom settings over
> several files is all that's needed (with a default arrangement that
> places all the package.el settings into ~/.emacs.d/early-init.el and
> everything else in ~/.emacs.d/init.el).

That sounds like an elegant solution (and it is also an argument for
having two separate files rather than a special `with-early-config'
form).

We would also want to consider whether people might want to place
config at any additional places in startup.el. We'd like to avoid
having more than two init-files, of course, so I think it's important
to try to capture as many use cases as possible with this new
init-file.

Probably, that means loading early-init.el as early as is humanly
possible, so that people can customize other points in the init by
adding things to hook variables.