GNU-devel and NonGNU-devel (was: A different way to interactively pass options to commands)

[Basil L. Contovounesios]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> Ah -- I only checked with `M-x list-packages', but it won't show up
>> there until there's a Version header in transient.el (that's bigger than
>> zero), I guess?
>
> Or until you add http://elpa.gnu.org/devel/ to your
> `package-archives`, yes.

Out of curiosity (apologies if these are already answered somewhere):

What are the exact differences in theory and practice between
elpa.gnu.org/devel and elpa.gnu.org/packages, and
elpa.nongnu.org/nongnu-devel and elpa.nongnu.org/nongnu?

Are the devel archives intended as (possibly WIP) counterparts to MELPA?

Based on which criteria are new versions of devel packages released, and
are they subject to :auto-sync in the same way as non-devel packages?

Can the two devel archives be used as drop-in replacements for the
default package-archives?

What are the pros/cons of doing so from a user's perspective?

Thanks,

-- 
Basil