If memory serves me right the protagonist in Inception was confused a lot and Wil can pull off confused.

Most likely Leo DeCaprio’s role.

With the squid machines doing hip hop dances in the background

Given that he turned it down for Wild Wild West, use that as a basis.

uh-huh yeah ha ha woo uh huh am I dreaming or is this real, sleep all day, gotta get that feel ha ha yeah oh uh the city is spinning, but ya see ha ha I ain't dipping. gotta get the reception, ha ha yeah woo it's an inception!

It is crazy how I always think of that movie as "early career Will Smith before he became famous quippy superstar" but it released between Men In Black and Wild Wild West.

There would be too many wisecracks. Did keanu even smile as Neo?

It would have been a very different movie. So, maybe people couldn't picture Keanu in that forgettable action comedy called The Matrix. But, Keanu did show he could do comedy. His first big movie was Bill and Ted's Excellent Adventure. He'd also done Parenthood. In addition, he'd shown he could do action movies / thrillers with a bit of comedy when he did Speed, and fairly serious action movies with Point Break.

Will Smith has done plenty of action movies, but all of them are at least somewhat comedic. He's shown he can do serious roles too, like Happyness, 7 Pounds, etc. But, I don't think you'd hire him for a science fiction action movie without having him do some comedy. I'm sure Will Smith could do a straight dramatic science fiction action movie with no comedy, but AFAIK he's never done it.

IMO Keanu is a much more limited actor than Will Smith. But, The Matrix played to his strengths.