"Tron: Legacy," like "John Carter," was a project that (barely) made it to screens before Disney decided to cut off their plans to take over the "boy market" (their words) with their own genre properties and instead just buy Marvel and Star Wars' catalogue. Both films got a mixed reception from critics and audiences, but "Tron" at least made money... though for awhile it seemed like not enough to justify a planned new set of sequels.
Apparently, that's changed. According to the Hollywood Reporter, the project is back on with director Joseph Kosinski returning to direct. No word on a storyline, though extra scenes and clues from "Legacy" point to Cilian Murphy (as the son of David Warner's human heavy from the first movie) having been set up for a larger role. Whatever, it's more Tron. I'm there.