The OPEN.<currency> stuff is a bit odd in that you do have to trust the coin you're buying actually exists, but from what I understand, it's demonstrable on the blockchain and is controlled by a smart contract. The OpenLedger team could explain it better than I, though.

The way DPOS works, you don't need that many nodes at all for very robust security. Some call that "more centralized" but I think in practice it's much, much better than a POW or POS system because those have not voting mechanism built in at all. If a bad actor (or many) start to hurt the community, nothing can be done. We've seen this happen already with miners controlling the future of bitcoin even if it's not in the best interests of the users.

Atomic swaps seem really interesting. I need to learn more about that.