Excelsior! Nowadays, Stan 'The Man' Lee is almost more famous (or, if you would prefer, infamous) for his eccentric personality and cameo appearances in the Marvel Cinematic Universe than anything else. That includes those he made in 2013's 'Phase 2' releases, Iron Man 3 and Thor: The Dark World, in addition to his brief stint as a clueless librarian during the high school fight sequence between The Lizard and Spider-Man in Sony's The Amazing Spider-Man (released back in 2012).
The Spider-Man/Hulk/Fantastic Four/Iron Man/etc. co-creator may well show up in all of the 2014 Marvel comic book movie adaptations, which includes the 'Phase 2' installments that he is executive producing - Captain America: The Winter Soldier and Guardians of the Galaxy - along with the sequel The Amazing Spider-Man 2. However, on the opposite side of the camera, Lee currently has a hand in developing a film project based around a brand-new IP.
Heat Vision is reporting that Lee, who turns 91 next month, has joined forces with Avi Arad - producer on the Spider-Man and Amazing Spider-Man films (among other Marvel adaptations) - for an upcoming theatrical release that is based on a new Lee creation. Lee's POW! Entertainment partner, Gill Champion, is also a producer on the film, with the search for a screenwriter (or two) to put together a script currently underway. Plot details and/or even a working title are being kept under wraps, as Arad claims that "Some titles give away too much."
If it weren't for THR's assurance that this project features a new Lee creation, it wouldn't be a huge jump to assume that the film in question is one of the potential Amazing Spider-Man spinoffs that Sony Co-Chairman Amy Pascal's mentioned recently (i.e. a movie based around one of the other superheroes/supervillains in Peter Parker's world).
For better or worse, that doesn't seem to be the case here; though, something like a Venom spinoff - which Amazing Spider-Man 2 writers Alex Kurtzman and Robero Orci have carefully hinted at - could very well become a reality one day. Not to mention, Amazing Spider-Man 1 & 2 director Marc Webb has strongly alluded to the possibility that Amazing Spider-Man 4 could be something different, like a Sinister Six feature (i.e. an Avengers-style teamup for Spidey's most dangerous enemies).
As for Lee's upcoming original project: best to wait and see if this one manages to move past the early stages of development, anytime in the foreseeable future. Things is, Lee's more recent character creations have tended to fall more on the 'Mad' side of 'Mad Genius'. For example, Nick Ratchet - a meek police officer who transforms into a video game detective - and The Governator (Arnold Schwarzenegger as Iron Man, basically).
In order words: there's probably a good reason that we haven't seen any of Lee's newly-imagined superheroes make the jump to the big screen yet.
The Amazing Spider-Man 2 swings into theaters on May 2nd, 2014.