Well, there's also some dispute over whether the policy as currently written does in fact demand that we exclude Vienna. The writer of that policy thinks it does, but we all know the danger of the intentional fallacy, don't we?
If a change in wording were needed to include Vienna (and, again, I'm not sure that it is), all we would need to do is make rule #4 say that we exclude a work if it is clearly intended to be set outside the DWU. Given that Big Finish itself is being equivocal on this subject, we could say that we allow Vienna because it's not clearly set outside the DWU. One word, if needed.