Just a few thoughts on and around the subject, not really in reply to anything or anyone in particular.
No, crews will (hopefully) never be able to skip the systems knowledge part of training. In fact, I'd to see crews be required to know more than they have to today - but the line has to be drawn somewhere, everybody can't know everything. Now, before I offend anyone, most crews have a high degree of knowledge of their machine's systems. It's in their interest after all, they're the ones strapping the things to their backsides. But it is possible to get away with knowing quite little and understanding even less...
The day they do get systems knowledge out of pilot training, I'll go by boat. Computers and comms do fail.
But the fact remains: Pilots know flying. They have to know enough about the systems to handle malfunctions and get the aircraft back on the ground safely in almost every manageable situation you can think of. But not more. And there are those situations nobody thought of. Sioux City?
Engineers have to know more. This means they're more able to figure out what is wrong with an aircraft. Sometimes, it may turn out to be something minor even though it seemed worse at first, or something easily solved. If so, the flight can continue - if, and only if, the crew agrees. It is their responsibility and their call. If it is not something minor, the flight should be aborted to sort it out on the ground. In that case, asking an engineer is not really necessary - but could be a smart move, air safety wise. Checklists and pilot training can never go into the kind of detail engineering training can - nor will engineering training ever include all the details of flying an NDB approach.
Safety involves taking all the information available that you can handle, pass it through what your training has taught you, give it as much of a think as there is time for and do what you think is best. In some situations (unexpected finding of Great White Shark in #2 fan at V1+1), there's no time to think or consult at all. In other situations there is, and it would be foolish to refrain from using an available source of additional information on the problem. What appears to be a "normal abnormality" at first look might well be something else. Something your training thought too unlikely to tell you about but which someone elses training might have included.
Every disturbance is a safety risk. The likeliness of having an accident is significantly higher during a diversion than during a routine flight. New airport, outside of the normal operation of the ATC system etc etc. So, if it was something minor which an R/T call to engineering could have sorted out, a diversion is putting passenger and crew lives at risk for no reason - not playing it safe at all.
I thought I was doing good trying to avoid those airport hotels... and look at me now.