The extrapolated volition of a cultural group might, given certain assumptions, resolve to a single set of values. If that were the case, you could express changes in expressed volition in that group over time as either progress toward or regression from that EV, and for various reasons I'd expect them to usually favor the "progress" option. I suspect that's what cousin_it is getting at.
I'm not convinced that we gain anything by expressing that in simple terms of progress, though. The expressed volition of modern Western society is probably closer to the CEV of humanity than the cultural norms of 500 BC were, but cultural progression along the metric described above hasn't been monotonic and isn't driven by reference to CEV; it's the result of a stupendous hodgepodge of philosophical speculation, scale effects, technological changes, and random Brownian motion. That might resolve to something resembling capital-P progress, especially since the Enlightenment, but it's not predictively equivalent to what people usually mean by the term.
And it certainly can't be expected to apply over all cultural traditions. The check on CEV described in the OP, however, should.
Taken from some old comments of mine that never did get a satisfactory answer.
1) One of the justifications for CEV was that extrapolating from an American in the 21st century and from Archimedes of Syracuse should give similar results. This seems to assume that change in human values over time is mostly "progress" rather than drift. Do we have any evidence for that, except saying that our modern values are "good" according to themselves, so whatever historical process led to them must have been "progress"?
2) How can anyone sincerely want to build an AI that fulfills anything except their own current, personal volition? If Eliezer wants the the AI to look at humanity and infer its best wishes for the future, why can't he task it with looking at himself and inferring his best idea to fulfill humanity's wishes? Why must this particular thing be spelled out in a document like CEV and not left to the mysterious magic of "intelligence", and what other such things are there?