gweinel
Explorer
I'm not sure it's all that rare. In my 32 years, virtually every group I played in had multiple people interested in GMing. The ratio hasn't usually been as high as 6 in 7 being more like 3 in 5.
The core of our gaming group which consists 5-6 gamers all wanted and DMed in the course of our 20 years of gaming history. However, the less hard core gamers of our group which consist another 6-8 gamers never had the patience and the will to DM. So, for my experience i would say that about 50% of our group DMs.