I have been thinking about these things a lot, and there is still some parts missing for what could really solve the issues. A community cryptocurrency is already out there and slowly spreading, absolutely worth studying. It's called Ğ1 and it's the first form of what the inventors call "free money" (as in freedom), analogous to the Free Software freedoms. This currency is based on the mathematics found in the Relative Theory of Money paper (Théorie Relative de la Monnaie, original in french). This moves the money creation from debt to the participant in a Universal Dividend, and seeing how Hive already functions it shouldn't be hard to recreate that fully.

I have two problems with the Ğ1 though for worldwide adoption:

1. It is built on Bitcoin and has the same scale and speed issues
2. It uses a Web of Trust that makes it really hard to get into.

Point 2 can be seen as an advantage to keep it to one specific community, but the problem is that Ğ1 is not easy to bootstrap for other currencies yet either.

Could a Universal Dividend coin and a good enough trust system against abuse of it (i.e. one entry per participant) be made on top of Hive or using the Hive code?

I was thinking myself that probably the Web of Trust could be replaced with a kind of reputation system, but as you talk about communities and we have SMT hopefully coming up, a SMT/steem-engine/hive-engine like system with a full WoT for a community could work just as well... We will just have to change among the communities.

I think we are very close...