GPL 6 doesn't say that you may place restrictions on some copies, as
long as your provide an unrestricted copy as well. Instead it says you
may place no restrictions.
You are being misleading. It actually says in part:
6. Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject
to
these terms and conditions. You may not impose any further
restrictions on the recipients' exercise of the rights granted
herein.
[continued]
So if I give somebody a DRM binary and an unencumbered copy of the
source and build scripts, I'm fine.
I don't think you can enforce DRM on GPL software.
There are plenty of circumstances where this might be useful: say, a
player application and a set of keys. Some not-very-useful keys are
in the source, and some very useful keys are on the DRM medium.