I might be wrong here (of course I might, because I don't/can't speak for the FSF, and I don't participate on the workgroup for free/libre distribution evaluation), but perhaps the whole point of the GNU FSDG is to answer questions such as: "Once a user sits in front of the system dinstribution being evaluated, how easy is for the distribution **iteslf** (or project, and those involved) to recommend non-(free/libre) software?"
Notice, however, that in such question, the focus is the average user, and so the thing that can "interface" directly with such user is a system distribution. What could be done (although risking being overwork) is: continuing having the GNU FSDG; but also make a Free Software Repository Guidelines (GNU FSRG). But this could also result in more confusion since we also have the GNU Ethical Repository Criteria that serves to evaluates code-hosting servicese (i.e.: not repositories to be used by [possible] free/libre system distributions directly).
