The site Collider.com has an article featuring an interview with TRON star Jeff Bridges (who played Kevin Flynn in the film), where Bridges sounds upbeat and enthusiastic about doing a sequel.
"But the reasons to do it and the reason I did that one (the original TRON) was because it was so innovative and I understand that they’ve got a whole new batch of stuff like that . . . innovations that they want to use on this so that could be kind of fun." - Jeff Bridges

Bridges is also quoted as saying "I hear they’re going to pitch me one (the sequel) pretty soon so . . .", but the tone of his speech indicates that he was joking when he said this. Or was he?

An MP3 of the interview that you can listen to, is available from the site. The interviewer asks Bridges about a TRON sequel, at approximately the 7:45 mark.

I noticed that the interviewer misinterpreted Bridges as saying "dancebell". What he actually said, was "dancebelt". Bridges was referring to the belts the actors had to wear, that were part of their "electronic world" costumes. The belts were uncomfortable for the actors, and Bridges was joking about them as perhaps being a reason not to do a sequel.

Thanks to Auric at TRON-Sector for the news.