I think it really depends on how much testing and training is required. The final piece of the track for SDD was put in place Aug 1, 2017 but the ride did not open to guests for almost another year. Even though we may see what appears to us to be a completed system, I'm guessing it will be a while after that before Disney actually opens it for guest use. I would love to be wrong but I think
@skier_pete's guess of 6 months is probably the earliest we'll see actual guests riding the Skyliner and personally I think 6 months is a conservative guess. I'm guessing mid-late summer next year before it's open for guests to ride.