Good question!
Could it be that 'this generation' (Matthew 24:4) refers to all the human beings that have been given the blessing to see God's glory through his prophets and lastly through his own son Jesus Christ?
I say this, because I guess I see Noah's time of destruction as the first time when God sets up a dramatic plan to destroy his creation because it failed to acknowledge Him - after which He promised never to destroy human beings through a flood again (so we could suppose there must be a time when his creation might be detroyed again, if necessary).
So I guess that when Jesus Christ spoke about this scenario of destruction and His second coming, He refered to the moment when God will put in motion his plan to redeem humanity for the second time. All human beings have had the chance to acknowledge God but haven't wanted to (Romans 2), after all.
Having said all that, I would say the promise of Jesus Christ's second coming is more accurate and real than ever, as we have already reached a point in which all humanity have become oblivious to God in ways never imagined. And our Creator must be utterly aware of it, right?