DAOs definitely will have focused on-boarding, and I think, we need to empower them better for onboarding as well as rewarding. For example @steemhunt already has got the necessary infrastructure to onboard someone pretty quickly. It also has the ability to reward them ( though how much may be questionable). 

And even though you say  not to talk about user retention and support, I think, DAOs need that ability, because only on-boarding won't solve the problem. Right now, OCD is looking for great content, but the DAOs objective may not be only great content. Take @actfit as an example. Many people will love to use it, but if there is not enough fuel for that, then the on-boarding becomes useless. 

And you can take care of on-boarding the great content creators, but that may not lead to mass adoption.