Smythe & The Spider Slayers
Who should play him? Phil Collins? Jean Claude Van Damme? Cher?
Why would/should they be included? Well, Smythe is a snidey little git who forever invents tech to wipe out Spiderman, including the Spider Slayers. He's always in major portrayals of spiderman in the comics, cartoons and video games soon enough, so why not the movies? He mutates from being in a bed/wheelchair to becoming a bloke who looks like an experiment went wrong with splicing snail DNA, which is ridiculous! I guess that would make sense if we really scrape the barrel and look at the first film and its video game, which seemed obsessed with human spliced with animal DNA- Lizard, Rhino, Scorpion, etc. But I don't think we'll ever see him in a Spiderman film.
Likelihood: Zero. Zilch. Zip. Nada. None whatsoever. It'd be kinda cool though, in a kitsch sort of way...