It says so right in the article: "In Bitcoin-NG, the protocol is, instead, forward-looking: every 10 minutes, NG elects a leader, who then vets future transactions as soon as they happen."
What if the leader goes down? What if 2 leaders get accidentally elected in the wake of that?
What if the elected leader is a bad agent?
I don't like non-leaderless decentralization schemes. All you're doing is adding mobility to centralization.
Keep in mind also that NG would be layered on top of Bitcoin, so everything that works in Bitcoin will work in NG as well.