Well, I've written a couple of two chord songs. I initially thought that these might make it easy for others to join in and play along. But instead, I have since found that the Pavlovian preconditioning of those who have previously been involved with three chord patterns found in blues, bluegrass, or even rock music often takes over, and that those who sit in or jam often automatically assume there are additional changes that do not exist. It's at that point that the song then starts to sound more like a train wreck. Ouch!
I like the concept of offering this type of musical environment, one or two chord songs, to those who love to solo. I've had the opportunity to have some wonderful soloists join me and a simple one or two chord background really allows those who have the ability to shine through.