I like the idea on face value, however there are pros and cons which need careful consideration to determine if this is actually adds any net value to the site.
I'm only going to cover a few here, to set the ball rolling, as there will be many pros and cons, and various issue within the systems that this could have adverse effects on.
- You flag a question: "unclear what you're asking"
- User edits their question and makes it clear
- You cancel your flag
On face value, being able to remove your flag after the user edits their question, means less clutter/incorrect flags in the review queue and saving reviewer time.
This only works if A) There is only your flag, or B) Everyone else who flagged (same question/same reason) also cancels their flags.
Neither are very likely
Lets say neither occur very often, as (A) valid flags likely have >1 flag by the time the user edits their question, and (B) most users wont check through questions they've flagged to see if they're now ok.
So likely you've done nothing useful to the review queue at all, and it's processed without your flag the same way with other users flags.
Being able to cancel will mean you wont get a rejected flag stat on your total, which in the above scenario that rejection stat is arguably unfair.
They are likely to occur
Lets say in the above scenario all flags are cancelled often (either was only your flag, or all other users with the same flag also cancel).
So great, the review queue is clearing up from unneeded clutter.
But, it's not that simple.
What happens to the screen when reviewing when someone cancels their flag?
Or if it was the only flag or all flags are cancelled?
It cannot remain, as reviewers might reject it, and then all users who cancelled their flags will be annoyed, and it also makes the proposed system completely redundant.
Worse would be that the reviewer accept the cancelled flags and the question is closed when it's been amended and possibly fine.
It would need to disappear, and reviewer gets a message "The flag(s) on this review have been cancelled. Nothing further is needed".
While they might be happy with that, with now less work to do, it's also possible they have just spent their time reviewing the flags and were about to take action.
Now move this into a realistic scale, where there are thousands of reviews to do, and the thousands of reviews are constantly changing because thousands of users are flagging and cancelling their flags.
How many times does a reviewer waste their time reviewing a flag for it to go away, before they get fed up?
It was the mouse with the dodgy DPI in the office
From accidental flagging, which does happen, I think that is probably your slap to take, to be bluntly honest.
As per your question, if you need coffee before being useful, don't flag until caffeine levels are adequate.
Sure, it happens clicking the wrong flag as they're close together, or your mouse is being a rat, but how often does this happen?
Using a new scenario of:
You accidentally flag, a complete and utterly wrong, irrelevant, and pointless flag, it was the mouses fault.
Also adding the fact that the ability to undo a wrong flag, means people will wrongly flag more, as they have the Ctrl-Z button they become less critical of getting it right.
(If they don't do that, then the entire proposal is pointless anyway - not enough occurrence to warrant it)
So now, how much simultaneous change can the review queues take before it all gets unmanageable, as it's never in any realistic static state?
With reviews coming and going, and flags being added and removed.
Flags still active for months
As for flags sat in your account which have been there months, this is a simple case of the review queues are under stress.
And while cancelling a now redundant flag would arguably be good for the site - reducing the aforementioned queue size issues - all the above I waffled about still stands.
What if others still have the same flag active, because the question was edited and no longer "unclear" etc.
Again, you are not saving the site anything as the other flags of the same nature still exist.
I think your idea sounds great, and I agree this could perhaps work, but with the systems involved, it's not just as simple as cancelling flags.
So your question/proposal needs to highlight all potential flaws, pros and cons, strong and valid reasons in favour, and everything else.
You might disagree with some or all of the above, however the point is it all needs to be considered, and ideally put in your proposal.
These and other potential scenarios have to be thought out, even if just to determine how likely or unlikely they are.
I guess this is why it hasn't received much attention, as you only offer an idea, without the whys and whatfors.