Disney has to do something about the lines. Keeping the experience as it is today just flat out doesn’t work well for new rides everyone wants to go on. So people miss out on riding the ride completely or have a miserable time standing in line for 3 hours.
Except Disney isn't doing anything about the lines. From what I understand (@marni1971 wink once if I'm accurate) they are not lowering the total number of available Fast Passes for an attraction. They are segmenting the total number of Fast Passes for an attraction into a Paid bin and Free Bin. Those wanting the free option will have to fight harder to get them, while those going the paid route should have a relatively easy time of securing high demand fast passes.
I would assume that those passes that don't sell get reallocated at some point. So in theory there should be no change to the number of FP users for a given ride, and as such the lines will either stay the same or get worse.