"IMNHO, 330/5.5 hour ETOPS is stretching the otherwise excellent idea a bit too far. "
Well, why is 330 minutes too far? Why was 300 minutes not too far? 180?
What would make it too far is neglecting to fully account for the failure modes and probabilities, mitigations, redundancies and so forth. If anything, the manufacturers and regulating authorities now have more certification experience and service history to go on than ever. With a properly computed aircraft performance, fuel load, plus the means to provide adequate electrical power for the required amount of time the airplane should be capable of reaching the planned diversion runway. The availability of the diversion runway, weather conditions and so forth are certainly challenges and the dispatcher must keep a wary and vigilant eye on them.