I think I could make a pretty good argument that delegates' "real world" identities being known by the community doesn't really matter or prevent a "Sybil attack". Imo, what would constitute a "Sybil attack" is the collusion of delegates' motives. I'm also pretty positive that the colluding delegates wouldn't "harm" the Bitshares' ecosystem, but instead use their power to manipulate delegate elections to capitalize on the delegate positions. Everybody can know everyones' name, but it's impossible to know their true intentions.
Any block chain has the problem that a few big players can collude, whether they are large stakeholders or large hashpoolers. We dilute that down to under one percent influence per delegate, max.
Then there's the question of what they can collude about. We can all observe whether they are performing their very limited block signing job to spec or not. We can look at their published price feeds. They have no other power.