Sounds like they have to ask for Moffat's permission every single time they want to use one or more of the Gang, so it seems
he's the main obstacle to a Paternoster series.
A licensee asking for permission to use Vastra, Jenny, and/or Strax in a story isn't the same thing at all as Moffat wanting to use Vastra, Jenny, and/or Strax in a televised product. Licensees, like Big Finish or Titan, even Panini in
Doctor Who Magazine and
Doctor Who Adventures, can't just do anything they want with their license. There are levels of approvals they have to go through. Characters and concepts like the Paternosters may require a little more scrutiny at every approval stage, just to ensure that the licensee isn't stepping on Moffat's own plans. Moffat, on the other hand, if he wants to write the Pasternosters into a script for series 10, there's nothing to stop him. That's just the reality of tie-ins, and it's something that anyone who's worked in tie-ins has had to deal with.
Moffat may well be standing in the way of a Paternoster Gang spin-off, but I'm skeptical that one has ever been seriously contemplated by Moffat and the BBC. For one thing, I recall Moffat saying essentially that "Deep Breath" was their last hurrah. For another, it's never been clear to me what the point of a Paternoster Gang spin-off
is. When
Ripper Street was in production, I could see the
how of a Paternoster Gang -- use and recycle
RS's sets and props -- but I could never see the
why. Who is the audience? What niche is it trying to fill? What can the concept do that
Doctor Who cannot? To me, the Paternoster Gang seems like the kind of concept that's ideal for the smaller, niche audience that buys the tie-ins but would be ill-suited to a wider, mainstream audience on one of the BBC channels.