Namespaces are not a problem as long as it remains a strict subset (i.e.main only) of Debian, and indeed fsf-linux user finding a bug in a package could presumably file it against the Debian BTS since if it is a real bug then it is also a bug in the Debian package.
Does your plan mean that FSF volunteers would only be able to introduce new packages by uploading to Debian?
Apart from the GFDL I am not aware of any licences which are DFSG free, but which do not meet the description of Free Software as used by the Free Software Foundation. (and there the issue is the other way round)
As far as I am aware, the FSF only regard programs as capable of being free software, so the above is not true.
-- MJR/slef My Opinion Only and possibly not of any group I know. Please http://remember.to/edit_messages on lists to be sure I read http://mjr.towers.org.uk/ gopher://g.towers.org.uk/ slef@jabber.at Creative copyleft computing services via http://www.ttllp.co.uk/