A point I've argued many times. But in hindsight I was somewhat wrong. No finite collection of fixed algorithms (Even a large set) can be ASIC proof (in fact, large sets probably just lead to ASIC monopolies due to higher NRE).  But if you change the POW periodically in ways which aren't predicable months in advance, and in ways that can't just be generalized with anything more specialized than general purpose consumer hardware... then I do think you would actually have achieved a fairly high degree of asic-proof-ness. There is just the question of the costs of periodic changes being worth the benefits, and what cadence is required to make investment unwise.