With the way technology is nowadays, I’ll admit to being surprised that the parks still haven’t been able to employ some kind of accurate system for estimating queue times.
I imagine that some kind of sensor-based system that counted net entry into and out of all three queue lines (Main Queue, Fastrack and RAP), accounted for set ratios of Main Queue:Fastrack:RAP and considered the throughput being attained on the ride to work out the overall queue time estimate shouldn’t be too complicated to implement (in theory).
That would ensure that queue times were mostly estimated correctly, assuming a roughly consistent rate of dispatches and discounting any occurrences such as breakdowns.