I was curious if this has ever been thought of. Somewhat obvious, to be honest, so it wouldn't surprise me if someone in Hollywood has already suggested this.
We all would love a sequel to IT, but we're not going to get one. Fair enough, as Mr. King is done with clowns. I respect that (actually, I wouldn't want so much a book as perhaps a short story follow-up in the vein of One for the Road).
Although I don't know much at all about the TV series Haven and The Colorado Kid, to the best of my knowledge (in fact, I perhaps had already discussed this on the board) Haven is basically used as a setting for more supernatural stories and is not really related to the book. So I was thinking that perhaps a TV series based on IT might be created. Call it The Losers Club. About the children of the original Losers, and how they come together to investigate/fight supernatural forces. Don't deal with IT (except maybe a second coming in the series finale) at all.
Perhaps this should be suggested to King if he hasn't already thought about it. Might be an interesting project.