I don't think you'll see any subjective difference in terms of the lines (FP or standby), or in how long FPs will last into the day, especially at the most popular attractions.
I think what will happen on average is that the standby line wait will be longer earlier in the day, and shorter later, but not to any noticeable degree.
But it could have an interesting effect on an individual's overall wait time during a day at the park. Since a guest would not be able to get FPs earlier to use later while they can get them more rapidly, and also taking advantage of the shorter morning lines, they likely won't be able to do as much during their park visit - and it could also potentially increase the total wait time for most guests because the lines will be longer earlier. I'm still trying to get my head around it, but that's what some thought processes are leading to.
