Yeah, return to a flat 30 seconds wait and just disable the damn button during that period so button mashing cannot occur.
EDIT: Mea culpa, I hadn't read the original link.
EDIT 2: Why would disabling the button encourage videogame like behavior? If you wish, incresae the limit to 45 or 50 seconds but leave the button disabled. This exponential increase makes no sense at all
EDIT 3: I personally doubt that disabling the button (done right) would confuse much, but I'd need an usability test to prove it (just like the other side of the argument.)
Is it so unreasonable to ask that people take 15 seconds to read, process, and think about what they're about to type before they post comment #2?
No, that is not unreasonable. What is unreasonable is that there is no way to know what the server will be doing and that you are effectively wasting people's time without giving a single warning or hint.
I guess nobody disagrees with the goal trying to motivate people to think about their comments and to preferably write only one comment. The disagreement is about the mechanism to achieve that goal.