Cho suggests that Neil Patrick Harris will be involved, although that hasn't been confirmed. Harris has become a bonafide superstar again with his role in How I Met Your Mother. He basically used Harold and Kumar go to White Castle as a springboard to his current success.
But there is one question that remains, the answer which could possibly derail the entire project, and that is Kal Penn's involvement. The actor, who spent time on Fox TV series House last year, left that show in order to take a job in the Obama administration. So there's a pretty big "if" hanging over the entire deal. I'm not sure how the Prez would feel about a member of his staff starring in a stoner comedy. If he had Tommy Chong serving as Secretary of Agriculture I'd say Penn's involvement was a shoe-in, but alas that ain't the case.
White Castle was one of the funniest movies I've ever seen. Period. This coming from somebody who has a natural aversion to stoner comedies. The sequel, Harold and Kumar Escape from Guantanamo Bay was less funny but a decent sequel. Not sure it's an idea that needs to be stretched further, especially using a worn out holiday backdrop.