Actually they did do a 5th anniversary in 2002 - but did skip the 10th. I thought it was due to no 'perfect 10' half runners but apparently there were a few - one on this board I believe. Anyway, the fastest a race has ever sold out was the 2002 half which sold out in less than 2 weeks.
I would expect a 15th based on the uncomfortable wink-wink I got from the runDisney folks in Houston last month.
We'll see
Here's photo of the 02 medal
& link as I cannot seem to get photos uploaded all the time
https://picasaweb.google.com/cewait49/OldDisneyMedals#550272663287716829