This leaves a lot of room for attack on a small number of nodes. Since most delegates probably won't have a state of the art computing centre to protect themselves, they will be vulnerable to DDOS attacks, among other things. If someone was determined to disrupt the confidence in the network, they would only need to go after the delegates once by one and take their machines out of the network. Of course the delegate pool would reshuffle each time with new delegates, but if good agents are taken out on a regular basis and bad agents have a chance to replace them, it would be possible to have a disproportionate amount of bad agents disrupting the network.
I don't think this attack is realistic. The blogger is underestimating the technical expertise of the delegates or the fact that knowledge/best practices will propagate over time. I think technical attacks is the one area where delegates will be the least vulnerable.
A valid attack against delegates that he mentioned is coercion. That is a viable attack but coercion likely will not work as most expect. Coercion would make make the delegate pool adapt to become coercion resistant over time. The coercion attack if it did happen is more likely to be extortion than to try to hijack the delegates because extortion would get the money from the delegates in the form of a hidden tax over an indefinite period of time.
In that case the extortionists would actually prefer their coerced delegates stay as delegates and that the Bitshares network remain stable. It wouldn't make economic sense for them to try to destroy a cash cow.
Selling votes and other forms of corruption/collusion may exist in Bitshares at some point and may already could exist in Bitcoin. I don't see any way to avoid that kind of corruption to be honest. But I don't think it's something to worry about right now when a delegate can't really make a fortune as a delegate and a lot of jobs pay much more than a delegate. I do think we could have a problem once the market cap and volume are high enough that delegates are living rich but I don't see how it will be more severe than the kind of problems anyone else with a high paying job would have.
The blog has some valid arguments many of which are known but haven't been discussed. I see a delegate like being on a board of directors at first but depending on the growth of the company then it can become a risk to be a delegate. At that point though the delegates could develop strategies to deal with those risks and being somewhat known may actually make some sense.
The gateway problem is actually the most pressing issue. We need IOU's at least for the digital assets. For physical assets it might present some legal difficulty but for bitBTC to become real would be very helpful especially if we could enter our BTC address in the Bitshares client and lock it to our account.