Wait times for standby ALWAYS have accounted for the high priority queue... because the ratio between LL and standby is always present. The standby estimes are already based on losing a percentage to the LL because this is a constant. If they didn't, they would be woefully under estimating all the time because nearly 3/4 of the attraction capacity is not going to standby.
I think what you are trying to say is the estimate isn't accounting for CHANGES in the VQs... which what would matter is when the ratio between LL and standby changes. The size of the LL queue doesn't matter as long as it's got people in it... what matters is the ratio used at merge. And when LL backs up, they increase the ratio of LL to standby which would delay standby waits.. which is not accounted for. But such changes are usually meant to be short lived...
Again, it's the ratio at merge that changes standby waits. A change that is dynamic and relatively short lived.
The wait time only has true meaning when you first get into line. The wait time for people behind you is meaningless in most regards. So the only place for Disney to radically improve that is during the period of time the merge ratio is changed, they could update how they are estimating standby. But unless you are entering the line during that time... such an improvement wouldn't mean anything to you.
No, the merge ratio also impacts the wait time for someone entering the queue.
Disney knows how many VQ slots are not yet redeemed and their WINDOW when they can be redeemed, but do not know when that person will enter the line... and honestly the scheduled VQs are not the problem. A scheduled VQ load would be predictable... and hence easily to account for as a steady constant. The problem is all the UNSCHEDULED people joining a LL queue and when they do so in waves.