It still isn't known if Joseph Kosinski will return to direct the Untitled Tron Legacy Sequel. Back in April, Joseph Kosinski hinted at several possible story lines for the sequel, although that was when Adam Horowitz and Edward Kitsis were working on the project. It isn't known if David DiGilio will build off their work, or start from scratch.
There is speculation that the Untitled Tron Legacy Sequel's fate may rest with the success or failure of the upcoming Disney XD animated series Tron Uprising, which is slated to premiere next year. Whatever the case may be, it seems we won't be seeing the Untitled Tron Legacy Sequel for quite some time, even if it does eventually get a green light.