It always struck me as odd that one of the original defining features of AWS never had a web interface. Maybe they were making it API-only to protect people from shooting themselves in the foot with exorbitant bills. Regardless through I'm really glad to see this finally!
I think another part of it is that an API interface actually makes more sense. While the necessity for the non-technically inclined are pretty obvious, auto-scaling shouldn't usually be done reactively, and doing so is at the expense of optimal service delivery. That said, I can imagine a good number of times it could come in handy, even for the techiest of us. It might have simply not been the lowest hanging fruit,…
You can react predictively (or predict reactively, whichever way you want to say it.)
Set up a cascade control system, training it as it runs on (process load x cost-of-scale.) It will begin to "see the signs" of load being about to occur, and adjust accordingly to reduce it. You know, just like any modern thermostat.