I was thinking, maybe in the case of posts that took under a minute (Maybe less, some folk are pretty fast typists... I don't know), there is an extra WARNING page which comes up first, maybe saying something like "Gee, that was fast. Hope this post came from your brain, and not your ass. Sure you want to continue (y/n)?".
a) This would not work for Quick Reply.
b) As a fast typist who can get a point across in a LOT less time than a minute (such as this reply for example), this would get very old, very fast.
c) tl;dr - too bad, but I think this idea sucks =P
EDIT: Bad Retro! Don't convert my point brackets into copyright symbols.