Stefan Monnier <monnier@iro.umontreal.ca> schrieb am Sa., 18. Apr. 2015 um 19:17 Uhr:

Maybe a solution is to simply make customize-set-variables lazier, so
that variables with a :require see their setting delayed to after
package-initialize was called. Or else, have package-initialize be
called by customize-set-variables. Or...

I would prefer one of these options over the other discussed in this thread. package.el and custom.el are now both part of Emacs, so there's no break in abstraction if they know about each other. It would make custom.el more complicated for the benefit of the users (who can stop worrying about the correct initialization order), which I think is a good tradeoff.