It is too early to tell. But really, using DHS as the example, there always was some de facto "tiering" if you tried to stack.
Obviously crowd size and the number of people who purchase the service will always affect availablity. But, if I attempted to stack at DHS, by the time I got to the third selection, availability for the "tier 1" attractions was pretty limited.
For example, if you made Slinky as your first choice at 7 AM and the park opened at 8:30, your second and third choices would be at 10:30 and 12:30. By 12:30 on a busy day availability for RNRC, MMRR, and MFSR might be gone or very late in the day.
Because we almost always go to a park at opening, our approach to this will likely be to make our 3 LL picks 7 days in advance and then target favorite attractions for park opening (including early entry). At DHS we have had good luck going TOT and RNRC first thing and if lucky might get to MMRR before the line is too long.
I will like not having to do the 7 AM login (some times done on a bus on the way to early entry) just to find out what time we can get for Slinky and ROTR. Knowing the times in advance we can then plan out what to do when the park opens.