IMO there is yet another angle to consider. I myself would think it could be understood in the same sense as the following passage. The following then, crossed my mind some time back when I was reading this passage.
Philippians 2:15 That ye may be blameless and harmless, the sons of God, without rebuke, in the midst of a crooked and perverse nation, among whom ye shine as lights in the world;
'Nation' is the same Greek word 'genea'. No one then should conclude a crooked and perverse nation/generation only applies to one period of time, such as 40 years. Of course the KJV renders it nation and not generation, but even so, no one would conclude it's only meaning in the midst of a crooked and perverse nation in a certain period of time only. Philippians 2:15 applied to those 2000 years ago. It still applies to us today. So when Jesus said this generation shall not pass until all these things are fulfilled, He's meaning in the same sense as this crooked and perverse nation. So IOW, when all things are fulfilled, so then will this generation be history as well since righteousness will now dwell because of the new heavens and a new earth.