One other advantage of the proposal: reduce the odds that people will downvoted and vote to close the same question at the same time. I looked at the data and that's happened about 800,000 times on Stack Overflow. Close votes should communicate: this question isn't answerable right now so go back to the drawing board and fix it. Downvotes on questions communicate . . . honestly, I have a hard time expressing what they should communicate. The tooltip mentions lack of "research effort", but wouldn't that be a good reason to close instead? If you don't yet have the close vote privilege, downvoting is a reasonable alternative, I suppose.

At any rate, it's likely that downvotes don't much matter to people unwilling to put in the time and effort to ask good questions. They can be crippling to those who try by editing. In addition, we have reason to believe that the more interactions people observe on the site, the more likely they are to ask again. So downvoting and closing might be more encouraging than people might hope.

Meanwhile, we have some precedent for wiping the slate clean:

• After serving a suspension, accounts are returned to normal.
• When a question is reopened, we remove the comments autogenerated by close votes. (Also the other trappings of closer such as the title change and post notice.)
• If a post is deleted (and doesn't meet certain criteria) reputation changes are caused by voting on the post are reverted.

The last is particularly relevant since a good way to avoid the cost of downvotes on a bad question is to self-delete it and re-ask. (Well, good until the system blocks you from asking.) Obviously, we'd rather people edit their question and get it reopened. So I like the idea of treating a reopened question as a new question.

[I'm still thinking about this idea. The goal is solid. Hopefully I'll have more to say in a few days.]