As I look at the new A350/B787 developments I can't help but wonder why they don't stick the engines in the back a la DC-9/CRJ? Benefits would be:
1. Lesser noise in cabin.
2. You can have bigger fans, which equals better economy without risking having them scrape on the ground and/or have to make tall landing gears.
3. Better view for passengers.
4. Lesser structure to support engines, thus lighter.
5. Less asymmetrical thrust problems.
Why is this design getting abandoned?
Ref #5. You'd think so, but it doesn't actually work out that way. It's true that there's less turning moment produced by asymmetrical thrust closer to the centreline but the designer, not missing a trick, will enhance operating economics (less drag) with a commensurate reduction in tail fin/rudder size.
In other words: an over-sized rudder for engine out controllability looses out to a smaller rudder for reduced specific fuel consumption.
From the perspective of asymetrical thrust handling, tail mounted engines have no advantage because the designer has built to aerodynamic specs which are good enough with anything better being detrimental to economic performance.
I've flown both the DC9 and DC8 - on a V1 cut the bootfull of rudder required to keep said aircraft going straight with the blue side up is about the same. Different engine configuration but a different size of rudder so the amount of applied boot is rendered equal.