2) Mathilda
In a way, this one did get made – just not in any way that connected it to the original, and not directed by or starring anyone originally on board. It opened as Colombiana, an action thriller about a young female assassin, directed by Olivier Megaton and starring Zoe Saldana; but long before that, the film had been developed as Mathilda, a direct sequel to Leon: The Professional.
The idea behind Mathilda was that Natalie Portman’s character from The Professional had grown up to be a successful bounty hunter in her own right, and was gearing up to get revenge for her Gallic mentor. The film was to have been helmed by Luc Besson, writer-director of the first movie; good job, because Portman was, apparently, up for doing this only if the original filmmaker returned.
Unfortunately, rights issues meant the film was canned, despite the fact that Portman and Besson were reportedly prepared to commit. Besson’s old studio, Gaumont Film Company, hold the rights, and apparently bear a grudge against Besson for leaving to form his own production outfit. Meaning a potentially great, female-friendly revenge sequel got shut down just because studio execs have no heart. Typical.