So... we've all seen the recent chaos caused by the license change from CC 3.0 to CC 4.0, and it's foreseeable that a similar disaster will occur when changing again to a future version of CC (4.1 or 5.0, just for example).
From my humble point of view, things could be precautiously eased by stating the license thing as such (or similar):
By posting on Stack Exchange, you grant us the non-revocable right to redistribute the content under CC BY-SA 4.0, and the right to change this license to any latest version available at a time.
This covers two points:
- The content is currently licensed under a specific version of CC
- The version of the CC license may be changed to the latest version available, at any time
- This, however, doesn't allow changing back, because 4.0 will no longer be "the latest available at that time" when a newer version is available.
Logically thinking, this appears like a feasible solution to me. It solves the licensing issue for once and for ever. I'm unsure what the community thinks of this.