This is all really valuable feedback. We've had the idea of displaying past changes to a post as something we'd want to add in general. This could let us implement that feature with polls in mind as a use-case.
Definitely will add a feature to prompt conversation post-vote. I think this can be dealt with through design choices and we'll see if we can split test to make sure we're having a good impact here.
You can do what Stackoverflow does: They have a grace period of 5 minutes where you can edit your post and it will not show in revision history (which is great for fixing typos and stuff like that), but any edit after that period is visible to anyone that clicks the "edited" link.
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