JWFan's own Jim Ware has posted a report from last night's Star Trek: Live To Projection concert in Lucerne which indicates that Giacchino (who was in attendance) will score not only Brad Bird's upcoming film Tomorrowland, but also one of the upcoming Pixar films!
MG: The next thing I'm working on is Jupiter Ascending, with the Wachowskis and then also Tomorrowland, with Brad Bird. I'm excited about both of them, because they are friends and it'll be a lot of fun. Also, there is a project I cannot tell you about. And, a future Pixar thing. I can't tell you about that either.
Owley: So, is that a project that hasn't been spoken of yet?
That was probably just a teaser / trailer cue, or some other such early stuff. Seems as though the main recording sessions begin today - which falls in line with this tweet from Giacchino on Sep 4, which indicated he'd be writing Tomorrowland in November
@m_giacchino Hello! Will you conduct the orchestra in Paris in november ?
@cloneweb - sadly no - I'll be home working on Tomorrowland and Inside Out.