This is interesting. I hadn't really thought about that. With Fast Pass+, they at least had a general idea of where a majority, if not most, of their resort guests were going that day. Without it? A reservation-free customer could go anywhere, and they may or may not have
Genie+, and even if they do they don't make the park plan known until 7 AM.
So this rezzie system is replacing that stream of data they used to get through FP+, kinda. You could take even one step further with resort guests needing to make 3 fast passes in advance, in one park. You're pretty confident that guest won't be hopping until after 2ish and their 3rd fast pass is spent. Hence the hopping rule.
I am sure this has already occurred to smart people. But thanks for bringing this up.