It appears that earlier reports of a new movie in the planned series were false. According to The Hollywood Reporter, Tron 3 is not moving forward.
In April, it had been announced that Tron: Legacy stars Olivia Wilde and Garrett Hedlund would be returning to their roles, with Joseph Kosinksi slated to direct. Shooting was tentatively set to begin in Vancouver later this year. Those plans have apparently been scrapped and now the entire production sits in limbo.
The sequel to the 80s classic grossed $400 million worldwide, which prompted trilogy talks.