The most ironic thing that never came to fruition was an X-Files spinoff [1].

The pilot aired a few months before 9/11. Depiction a plot by the (I believe) CIA to crash a passenger airplane into the WTC. And the three computer freaks/conspiracy theorists that often helped Mulder trying to stop that.

I watched it a few months after 9/11 happened. That definitely was an experience I will never forget.

Even as a German, 9/11 for me ranks in the top three defining historic moments that I actively remember that demarcated the timeline in a clear before and after. Next to Chernobyl disaster and 11/9 (fall of the Berlin Wall).

Edit:

[1]: https://en.wikipedia.org/wiki/The_Lone_Gunmen_(TV_series)