It'd need to be clearly marked — the promise we make in Debian ``main`` is quite strong: if you install it, you can use it for any purpose, modify it, share the changes with your neighbour, etc.
And (although not explicitly codified, we touch on it in "must not contaminate"), you can install Debian on a system, install any package in ``main``, then clone the resulting disk and redistribute it as an image. This precludes having things like ``zfs`` in ``main``, as (last time I reviewed it), it was pretty clear that the resulting combined work was probably not redistributable.
(N.B.: I'm on the team that maintains ftp-master.debian.org, and reviews all new software for DFSG-freeness, amongst other qualities)
And (although not explicitly codified, we touch on it in "must not contaminate"), you can install Debian on a system, install any package in ``main``, then clone the resulting disk and redistribute it as an image. This precludes having things like ``zfs`` in ``main``, as (last time I reviewed it), it was pretty clear that the resulting combined work was probably not redistributable.
(N.B.: I'm on the team that maintains ftp-master.debian.org, and reviews all new software for DFSG-freeness, amongst other qualities)