>but we'd have to have communities that do those first.

It will arrive. just think about now (before) they have to do drives for SP delegations for their users. Pass around the hat so to speak. Delegating SP loses voting power so is harder to give away than 'unused' bandwidth. 

>There will also be people that come here knowing nothing...so we would have to watch for new users that show promise, if we limited people too much.

The community could welcome in with a better onboarding system meaning the users come in understanding the suggestions. A few front end tweaks would solve a lot of the Spam before it starts. 

>There will also likely be communities that don't necessarily know if the people that register there are going to be quality posters...

The community itself starts to police itself and doesn't need to use flags to do so.