A third installment in the TRON movie franchise was reported to have entered development around mid-2010, several months before Walt Disney Pictures released TRON: Legacy - the belated sequel to the cult 1982 adventure about a programmer (Jeff Bridges) who must fight for his life after entering a digital world known as The Grid. Legacy wound up being a moderate critical/commercial success, which wasn't enough to get TRON 3 fast-tracked... but enough to keep hopes alive that the film would get made by the Mouse House, eventually.
Jump ahead to March 2015 and new reports emerged - claiming Legacy director Joseph Kosinski is in the midst of preparations to start production on TRON 3 in Vancouver around September or October. Well, sorry to say TRON fans, but for the time being it appears as though that's not going to happen after all.
Multiple outlets (including THR) are reporting that Disney has pulled the plug on TRON 3, though it should be noted that sources claim the project had never received an official green-light. Kosinski was expected to return as director on the third TRON installment, which would've picked up a few years after the events of Legacy with Sam Flynn (Garrett Hedlund) and Quorra (Olivia Wilde) - the latter being a program created in The Grid, who had made the jump to human form by Legacy's conclusion.
THR's report on TRON 3 being canceled also mentions that Disney had been interested in adding Oscar-winner Jared Leto - who's currently playing Joker for David Ayer's in-production Suicide Squad movie - to the cast in an undisclosed role. However, talks with Leto never actually happened and a proper offer was never made - so, whatever role the actor was being eyed for remains a mystery for the time being.
Many TRON fans were eagerly anticipating TRON 3 being made, based on the hope that the film would deliver more of the shiny visuals and exciting Grid-based action sequences (see: Light Cycle races, Disc Battles, etc.) offered by Legacy - but, paired with a stronger narrative than the second TRON movie's.
Of course, TRON 3 would've been another big-budget gamble of sorts for the Mouse House - as Legacy didn't make as much at the box office as the company had hoped for ($400 million on a $170 million budget, not counting marketing). It's less surprising that Disney has decide to not take the chance with TRON 3 for that reason, especially now that Brad Bird's Tomorrowland looks to become the company's latest costly live-action tentpole to disappoint financially (following John Carter and The Lone Ranger).
It surely doesn't help that live-action features such as Kenneth Branagh's Cinderella have recently outgrossed Legacy at the worldwide box office, while costing a good deal less to produce/market; even the upcoming Pirates of the Caribbean: Dead Men Tell No Tales (the fifth Pirates installment overall) will probably sell a lot more tickets than TRON 3 would've, but not cost a whole lot more. So, the sad truth is, moving ahead with another TRON film wouldn't have been the smartest choice for the Mouse House to make, purely from a business perspective.
Disney will instead be moving ahead with safer bets than TRON 3 over the next couple years - including, more live-action remakes of titles from their animated film collection (The Jungle Book, Beauty and the Beast), additional Pixar feature films, Disney Animation Studios projects, more Marvel Studios films, and (of course) several new Star Wars movies by Lucasfilm. Suffice it to say, the Mouse will remain as rich and powerful as ever for the foreseeable future.
As for TRON fans - it is too bad that many got their hopes up about TRON 3 in recent months, only to have them be knocked down so quickly. At least they got to see The Grid brought to life via modern CGI and 3D filmmaking techniques in Legacy (along with a rockin' soundtrack by Daft Punk). And who knows, maybe everyone will get to revisit that world again in some form (comic books? Maybe another cartoon TV series?) somewhere down the line.