Hi all, thanks for the feedback.

I will put json-mode.el into GNU ELPA, then, with the minimum required
version of Emacs as 25.1, and package version lower than Josh's
json-mode.el (for instance 0.1).

If I understand correctly, it will show up in the package menu, but
Emacs 24 users should see an error message if they try to install it,
and users of the existing json-mode.el from MELPA shouldn't be
bothered by the new package.

How does this sound?

-- Simen