HarryMann:
Well, a very cheap and cheerful but extremely useful modification would be one or two vidcams around the plane, with the ability to flip a screen from one to t'other; a wide-angle view from top of fin, and along the belly (and possibly looking inwards from both winglets, if fitted)...
The unfortunate thing is that it sounds cheap and cheerful in theory, but then you have to factor in the number of DC-9/MD-80/90/717s currently in service, of which a significant number are well past their median service life. It's not just a case of fitting cameras too - you'd have to retrofit a sturdy area to the airframe to attach them, they'd have to be reliable enough to deal with the rigors of extreme temperatures and moisture levels, and you'd still have to plumb the camera output back to the flight deck and affix a suitable display.
These costs add up, and on this particular model there's a perfectly good gauge telling you the surfaces are deployed - and it seems like there's an equally good 'killer items' check that should be performed before the take-off roll that should maybe considered mandatory on this, if not all types. At the end of the day, a pilot under sufficient pressure could still miss the camera as a final check, so really you'd just be providing another backstop.
Having said that, the ease of switching some aircraft systems into 'air mode' does trouble me, and I wonder if a non-functioning configuration warning system ought to be a no-go item. However, as an admitted non-pilot I wonder how practical that would be.