Good question.
It does absolutely not require your playbooks or modules to be GPLv3.
Playbooks are data and are yours, and are modules. Same true of any
inventory scripts you write, as they are simply executed. (Callbacks
and server side actions of course don't have this luxury, but if you
are not distributing them, this is not a problem, and only requires
that you redistribute source for them if you do... so no big deal)
I have been thinking it may be reasonable to make just
lib/ansible/module_common.py (which is not part of the rest of ansible
but really a utility) BSD just to prevent any doubt of this, please
yell if any active contributors to specifically that file (and only
that file) object and I'll make it so ASAP.
--Michael