The reliabilty is a big factor. I do not doubt that it'll be possible to design an aircraft that can fly half-way around the globe without aircrew however; I don't have much faith in computers. It must be that I posses the magic finger that makes them crash, whether it is Win98, 2000 or even the FS Emb 145 sim crashes once in a while. The V-22 crashed due to a software error.
But how long will this plane last? The older electronics get the more problems there'll be. Looking back at my flight school days, there was not one week where we did not have an inoperable King transponder. If a transponder is not even built to last a week within its five to seven year lifespan, what about more complex avionics? The Citation V Ultra I flew for a short while liked to be flown to the Citation Service Center.
Finally, take a look at all the ADs issued for transport category airplanes: Within the first few years a ton of bugs have to be sorted out. With the new generation glass cockpits, I highly doubt that there'll be an error-free operation. The main job of the aircrew in the future will be to perform airborne warm and cold resets ...
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