William Shakespeare's Othello: Shakespeare's controversial "jungle fever drama" (not actually a real expression) has often raised eyebrows for the casting of white men in blackface in the role of Othello, the Moor. But the crazy gimmick behind this bit of stunt-casting would be the racially appropriate casting of Will, and the color-blind casting of Jada as Desdemona. In fact, if Alfonso Ribeiro can free up some time to take on the role of Iago, this could actually be the best Othello New York's seen in a while.
Molière's The Imaginary Invalid: Will played a brilliant doctor who accidentally caused the end of the world in I Am Legend, and here he'd play Argan, an aging hypochondriac obsessed with his disastrous medical bills and trying to set his daughter up with a doctor. Jada would play said daughter, Angelique, who's to marry a successful Parisian doctor so her family will get free medical care. It's the perfect comedy for the age of healthcare reform.
Samuel Beckett's Happy Days: The appeal of taking on this bit of masterfully bleak modernism is that Will would be reduced to little more than a prop: the male character in this two-person existentialist tour-de-force grumbles incomprehensibly near the rear of the stage for two thirds of the play, masturbates, and then walks away never to return in the middle second-to-last act. Meanwhile, Jada sits partially buried under a pile of rubble (first up to her waste, then to her chin), spouting inane thoughts about everyday minutiae and occasionally breaking down into hysterics before collecting herself. Not very glamorous, but gutsy as hell.
Sam Shepard's Fool for Love: Can you picture these two fighting ever? I mean really yelling at each other and saying horrible, hurting things to one another? No, and that's why to see them go at each other (angrily, then sexily) in Shepard's motel-set drama about quarreling lovers would be so perversely enjoyable.
John Guare's Six Degrees of Separation: This one's fun because Will already knows it for having turned in one of the best performances of his career when it was adapted for the screen in 1993. Here, however, he'd take over the part that Donald Sutherland played in the film, of the Upper East Side aristocrat who, along with his wife (Jada, obvs), are taken for a ride by a young gay drifter who claims to be their son's best friend, and the disowned love child of Sidney Poitier. To complete the role reversal, a white actor would be cast as the fraudulent house guest, and would claim to be the illegitimate child of, oh, let's say Mel Gibson.
Bonus: Men In Black: The Musical
Ya know, given that Spider-Man is being made into a musical, this actually isn't as great a stretch as it may seem. In fact, turning this comic book-adapted movie franchise into a stage musical makes a million times (or, $50 million times) more sense that Spidey. Think of all the great alien costumes, the wacky, Cats-like musical numbers in which each interstellar refugee tells their story, the funny repartee between rookie and veteran MiB. Heck, they've even got the first song ready to go: