Wait times should not be significantly different. When people have a fastpass, they aren't in the standby line. The same number of PPH will be going through. More people don't magically come to the park and want to ride Falcon because suddenly there is FP.
What also will happen is that peak times will probably decrease a bit, and off peak times (say, night) will increase a bit because FP spreads out crowds throughout the day, so you can't look at single point in time comparisons. But average wait time across the whole day will be fairly static.
That's the basics of queue theory anyways. Based on what I've seen I think that's the case. But the data sets we've had have always been imperfect comparisons. Now we will have a much more direct comparison to finally put to rest the debate of whether or not FP actually significantly affects wait times or not. There may be a small increase or difference (or even decrease), but I would bet that it won't be much different than similarly crowded days before FP. As a data geek, I'm excited to see what happens here, and prove my argument right, or, possibly prove it wrong. But seeing the actual data and comparing will be fascinating as it's really the first opportunity we've had to compare since FP was introduced, and there were a ton of other variables in play back then that potentially skewed the data set.