(I used to send Email from gnus, but I have already lost my gnus
settings and will reply from Gmail. I hope I get it right.)
> There was talk of integrating leaf into use-package a year ago.
Nothing is going on with integrating leaf and use-package as no
one is working on it. Honestly, I don't like use-package because
it has surprising behavior that often seems nosy. That is why
leaf was created, to organize/reduce the features that
use-package has and to give user a better interface, which is
why it cannot be integrated.
On the other hand, I agree that leaf has a puzzling internal
structure. It has huge conditional branches directly in a list,
dynamically generating S-expressions and eval'ing them. This
structure makes debugging difficult and adding new features
difficult for new people. (I can do it, though.) This is why I
am hesitant to have it standardized in Emacs.
In summary, the functionality that use-package already provides
should be sorted out because it contains magic. The interface
provided by leaf is pretty, but it has a puzzling internal
structure. I would support a third use-package that should come
standard with Emacs, if there is one. And some people said that
the name "LEAF" is a bad name. Hopefully the third use-package
will have a better name.