Re: the repurposing of an airliner...
IIRC, the Pilot episode of the X-Files spinoff, The Lone Gunmen had that very idea
Yes. Specifically it was based around a conspiracy to hijack a passenger jet and fly it into a prominent New York skyscraper. The hijacking was electronic (using the magic computer technology so beloved of TV shows) and the skyscraper was the Empire State Building, but the similarities to the actual 9/11 plot show just how unimaginative the latter was.
& had to be shelved for a while due to 9/11...
It was broadcast in March 2011. The entire run of The Lone Gunmen was over by June of that year, months before the attacks.
Incidentally, from the article:
the repurposing of an airliner as a weapon would definitely have been seen as movie-plot stuff until it actually happened
Yes, every event that hasn't happened yet would be fiction, until it does happen. That's how reality works.
And before someone objects that not all fictitious events are suitable for movie plots: I submit the last several years of the film industry.
 We hear a lot (at least in the US) about "terrorist masterminds"; but historically they've been largely unimaginative, not very smart, and hugely inefficient. Yes, 9/11 had a nasty body count and huge property damage, and the indirect costs were enormous. (And not always apparent; I've seen reports that the damage to US agriculture from redirecting resources away from pest control to terror defense is now over $100B.) But given his resources, OBL should have been able to achieve much more, particularly after 9/11. It's not like he lacked models - the "Beltway snipers" managed a good run of terror in the DC area with two guys, a rifle, and an old car (and they'd have done much better if they hadn't tried to extort money), and there's a ton of public research on potential security attacks. Terrorists get lucky sometimes because perfect vigilance is impossible, but all evidence suggests they mostly suck at their jobs.