Your point is fair. I think the time that people could commit to a controlled experiment would be a limiting factor.
I think it would be interesting if people used the post as a jumping off point to do informal experimentation, and they could take the time they thought it would require. This would not necessarily yield the same precision that a randomized trial would, but as per your point, there may be a tradeoff between external validity (taking the time to really practice the faith) and internal validity (limits on time commitment in the context of a randomized trial to gain causal inference).
First, thank you for enjoying the proposal. In addition, I simply did not know that there already were religious communities for EA, and I find that interesting.
I think the proposal still has potential in terms of identifying communities that do not self-select into EA but where EA could take hold if socialized.