I kinda think that if cancellation still resets your booking eligibility, it doesn't really allow for rolling over your multi-reservation stack, and that's the whole value. There's no point in waiting to build a multi-reservation stack unless either you're going to arrive to the park later (and that still works), or you can keep your two reservations all day by leapfrogging them. You can't leapfrog any more, so there's typically no point in deliberately creating a stack. You could just book reservations and use them during that time.
See, I think you could still set up an ongoing double stack, but in a much more restricted way. The trick would be to only book return times within 2h of the booking time, and then make sure you tap in before the 2h window is up. The cancellation makes it possible (in theory) to get to the initial setup of two active LLs, each within 2h of its own booking time.
Of course, they could be tracking the booking time of the original reservation across cancellations, but that seems a lot less likely.
I'm not suggesting that this would have much practical value (if any). Maybe it could work on a quiet day, if you're not too worried about riding a lot of headliners. But in that case, you're probably just as well off repeatedly rebooking your single LL, as intended. Still, I think it's probably technically possible, and I just like to understand these things.

What they've done here is actually quite clever. Both simple to implement and very effective.