I'd say there's a strong consensus that you can form a work that combines (3-clause) BSD-licensed and GPL-licensed content and distribute the result under the GPL - the FSF has been publishing its list of "GPL-compatible" and "GPL-incompatible" licenses for decades now, and copying BSD-licensed libraries into source trees (GPL and otherwise) without changing the license of the whole for a similar length of time. I'd agree there probably isn't any kind of clear consensus about what happens in the case where there is no substantive GPLed contribution in the first place, because that doesn't seem like a case that would come up very often. (To me it seems obvious, but I guess to other people some other interpretation might seem equally obvious)