So basically you're using PID as a metaheuristic to guide an optimization process? (like particle swarm, simulated annealing, genetic algorithms, etc)

Or it's more like, it's being used to fine tune the parameters of another search procedure? And in principle you could use a neural net rather than PID (that would encode a surface that matches the latency vs search depth profile that you want)

edit: just figured out those two are the same thing; the PID is optimizing the search depth for a given target latency