There is already a grace period of 10 minutes, after which all further edits are visible for everybody. I’m not sure if it only works for ordinary posts.
See also: Updating the original post is a problem for email users
I don’t understand. The existing visible edit history already provides that.

(or even requiring edits to be approved by the original author) would be fantastic.
This doesn’t scale. The author should not be forever responsible for the post, they should have the right to free themselves from this duty.
Edited the title by adding “for wiki posts”.