Except this only works if all rides are equally attractive. If you get a fastpass for a ride that normally has an hour wait (bringing your wait to 20 minutes), you are then able to used that saved 40 minutes to do two more secondary rides with waits of 20 minutes each. The secondary rides also have fixed capacity, and now there are more people trying to go through them (if you hadn't had that fastpass, you wouldn't have tried to go through the secondary rides), whereas the person who only got a fastpass for a secondary ride (say wait time is now 5 minutes) only saved 15 minutes, which isn't enough time to add another ride to their day. Now, if there was enough ride capacity for each guests to do every ride once per day then it would work itself out, but I don't know if that's the case. Considering everything that is currently closed (meet and greets and shows that would normally spread out the inflation effects of fastpasses at the better rides), if you added Fastpass right now in its previous form, it would undoubtedly be great for a the lucky few, and terrible for everyone else. To me that is why a paid system makes sense - that way at least people are paying for the better experience and not just getting it through luck of the draw.
The system as it stood before would also penalize people who take last-minute vacations which I would think is the very last thing Disney wants to do. It's hard to entice people to book a trip at 60 days when they aren't going to get on any "good" rides (and, although I know this forum is full of people who plan 11 months in advance, there are people who don't plan so far out).
In my mind, it is a no-brainer that Disney will move to a paid system. I still believe there will be free options, but I will be very surprised if there isn't a way to pay to bypass the line while in the park. I wouldn't expect any form of fastpass to return until the new system is ready. I don't think it would be good from a marketing standpoint, and I don't think it would even help most people because of everything that is closed.