Just to frame the problem slightly differently, if you had unlimited number of humans who could perform tasks as quickly as a computer this wouldn't be a problem need solving. So since we know that's the end state for any human-in-the-loop system then maybe it's worth solving that problem instead.

A few things come to mind, divide the problem into chunks that can be solved in parallel by many people. Crowd source your platform so there are always people available with a very high SLA, just like cloud servers are today.