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.
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.