User blog comment:Jacknapier10/Which characters cannot appear in the Marvel Cinematic Universe?/@comment-5350299-20140428113836/@comment-24901406-20140505131622

Theoretically yes, but they'd need to be careful because Sony could be upset with Marvel setting up competition/stealing the audience/whatever which could create problems and a rather nasty law suit (see Mutant X for an example of this). I doubt we'd ever see Spider-Man while the film rights are away (otherwise people might expect to see him appear in the films, or assume the Sony films are part of the MCU) but other characters tied up with the rights (such as Kingpin) are absolutely possibilities.