It would appear that a TRON graphic novel was once planned, to be published by a company called Cho-Zen Publishing. As proof, I was sent a link that allowed me to see mock-up front and back covers of this graphic novel, which hint that it was going to be an adaptation of the movie's story. (However, I will not post the images or the link to them, since I do not have permission.)
What leads me to believe that this is a past project that was canceled — as opposed to a current project that is upcoming — is the following.
- Doing a search on "Cho-Zen Publishing" (or "Books") reveals that they only have one published comic to their credit, called Shao Tzu, dating back to 2003.
- SLG is the current rights holder for comic books related to TRON, so any new books would likely be coming from them and not another company.