RE: Will the other interfaces offering communities support use Steemit, Inc. Hivemind node(s) or have their own?

Unless they change any critical logic, we can all run the same nodes and be in sync. And I would strongly encourage any changes (caveat: which make sense for most/all UIs) to be added to core. I'm sure some apps will want to extend communities with "extravagant" features, and that's great, but we need to make sure core does not get bloated.