Last September a lot of us were concerned with the decision by Stack Exchange to unilaterially change the licences on previously-submitted user content, which is against Creative Commons' guidelines and the terms of the licences themselves.

Tim Post has finally responded:

We are still investigating the question of substantial edits to content licensed under CC BY-SA 3.0 now that we’ve switched to version 4.0. For the time being, pending final clarification on this, content will be listed with a license based on its creation date. This would mean if a question or answer was created under CC BY-SA 3.0, revisions to it made today would also be released under CC BY-SA 3.0, not 4.0.

And that:

Your feedback made it clear that your concerns were mostly about the way the change was handled, and not so much about any specific version of the CC BY-SA license.

This seems like the most pragmatic way to go, though I wonder why it took six months of silence before we got a formal response.

I don’t submit to those sites anymore; I advocate people posting on platforms they control. But SE is a huge resource, and the clarification is welcome.