This isn't the first time it's been indicated that B.A.R.F. will be used during Avengers 4. In addition to other set photos showing cases labeled B.A.R.F., it was rumored last fall that there's a scene in Avengers 4 where Tony Stark is running a simulation with Harley Keener (the kid from Iron Man 3) to study Battle of New York and figure out a way to use the Tesseract against Thanos. However, I still have my suspicions that time travel will factor into Avengers 4 somehow. While B.A.R.F. can certainly explain how some of these past events are revisited, the technology also works off memories, and Tony Stark wasn't around for moments like the battle against Crossbones in Lagos. So unless Tony's bringing in some of his fellow heroes to share their memories, which is certainly plausible, we shouldn't entirely discount yet the idea that there will be some temporal shenanigans in Avengers 4, presumably via the Time Stone.