You can't do that automatically without involving a centralized third party, that would have the authority to pronounce when it's known that the algorithm has been incorporated into ASICs, and then the power to make all nodes switch algos. You could use social consensus to convince people to fork, but what's the point? Somebody would produce an ASIC with the second algorithm, and the third, and the fourth. How many forks you and your community can tolerate?
It's more productive to concentrate research on how to design ASIC-resistant algorithms overall. Some solutions have been proposed, but it's an arms race, there's always room for improvement.
If you are saying to that extent, true absolute pure decentralization is not really possible. For bitcoin there is also centralized aspect of it. Mining is most common example. Also development of crypto coins are highly centralized, it is open source but still there are select few are qualified to contribute.