I think, we want to do somehow both, but more the latter (if I understood you correctly). We’ll develop a software, which enforces some central constraints (“Q&A platform”). It will be possible to host multiple, independent communities within one software instance. Each instance and community can overrule our configuration presets for most details (text, triggers, variables, rate limits, …).
Furthermore, we’ll be hosting one instance with multiple communities. We’ll give this instance a bit more support/assistance/… of course, but the communities are largely free to do what they want (within a reasonable limit - our simple Code of Conduct and legal stuff will have to be kept).
If I recall correctly, we plan to also have some kind of instance-level decisions by the community, such as having a review panel, which is elected by the community members and serves as a way of appealing moderator decisions and reviewing their behavior and possibly removing their mod status if needed.
We had some long-ish thread about what we are trying to build. If you have 75* minutes to spare, you can read through it. 
* estimation by the forum software