Nothing should change with regard to fastpass lines. If anything, they should get shorter.
The fastpass system is distributed the same as before. Only a certain amount of people could get fastpasses for a certain time. Then it moves on to the next 5 minutes or whatever. That is the same for FP+.
The only thing that will change the length of lines is if participation increases or decreases...and from what I've observed, very rarely, if ever, did fastpass- times coincide with real time. There was almost always an hour gap at the least between pulling the fastpass and riding...which means lines can really only get shorter. The only other variable is fastpasses that get pulled but not used...which, once again, I would guess will increase with the new system...which would cause shorter fastpass lines.
This system is being a bit overcomplicated. The only thing that has changed is distribution amongst guests (no guest can use more than 3 to cut down on some guests having a higher fastpass ratio than others), and the system is now digital and selections are made further in advance. The rest of the system is largely the same.