Many loyal WDW guests / fans (myself included) have been spoiled by short waits on popular attractions via FP+ and short-to-medium waits for less popular attractions without needing to rely on FP+.
A 100% paid FP system (especially one that is as expensive as has been rumored) would mean that many in the aforementioned group would instead have “medium-to-long” waits on popular attractions, and “short-to-medium” waits on less popular attractions.
If you are wealthy enough and willing enough to pay up for FP, you will likely be happy under the new solution. If however you are someone who has historically made the most of FP+ (like many on this board) but are not wealthy / willing enough to pay up for FP, your experience at the parks will likely be worse than it was under FP+.