Bottom line is there is one reason and one reason only that Disney will roll out any changes and that is that it will increase its profits over the long term.
They aren't necessarily thinking about a year or two, but 5-10 years away what today's changes will mean for profits then.
As for selling out, my guess is that Disney will hold a certain number of reservations for day of (which is what they should do for the restaurants as well). This will prevent them from being completely sold out.
I would also imagine the 3 limit will be 3 per day in advance and then day of will have similar limitations to what the current FPs have. They could even make it where park hopping isn't restricted for day of reservations.
They aren't necessarily thinking about a year or two, but 5-10 years away what today's changes will mean for profits then.
As for selling out, my guess is that Disney will hold a certain number of reservations for day of (which is what they should do for the restaurants as well). This will prevent them from being completely sold out.
I would also imagine the 3 limit will be 3 per day in advance and then day of will have similar limitations to what the current FPs have. They could even make it where park hopping isn't restricted for day of reservations.