What I’d like to try, though, is the approach presented in Stephen Wendel in “Designing for Behavior Change: Applying Psychology and Behavioral Economics”.

I'll have to look that up, I'm not familiar with the author or the book. That said, I've found people will want to stick to their favorite thing rather than the most important. I think that's why having a leader of some type is important, but it's awkward if you're working together on somewhat even grounds (like a bunch of friends starting a business).

I think having someone step up and making sure other people stay on track is important, but the problem is if you feel too much like a superior or useless management then the whole thing just becomes a horrible experience for everyone involved.