You can already do this by mining at an auto-switching pool using Claymore. What would be useful is for Claymore to auto-switch POOLS based on profit, he can dream big and combine all his miners controlled by a separate program that looks at the pool API's and starts the appropriate miner.
Can you imagine hundreds of thousands of miners hitting that API?
How do you think the nicehash miner works?
Nicehash isn't a free service. They are paying for bandwidth/resources by the fees.
A public API is going to have costs / overheads.
Claymore wouldn't need an API; the switching would be done locally and you access the APIs from the pools. A local controller app would launch the miner(s) and connect to them via the 'mport' to tell it what pool to use. If all the miners had a benchmark feature as well, it could determine the speed for each algo to base the profit calculations off. This is all that Nicehash do but they lock it to only their pool's API.