1. Agreed, discussion posts remain as it is, with the 10m window (in case you want to correct errors and stuff like that).
  2. Main posts, like long posts, guides, essays, lists etc I would like to have them fully editable. I would not be so crazy to change the whole text, will be just small updates maybe, in time, if something became obsolete or were some mistakes that other readers point them out etc.
Is it nice to have like a small footnote with history changes? Maybe, but that could clutter more the SN database I think. And for what? Just for few readers that will click it for curiosity? Keep it simple.