If a coin/algorithm becomes popular somebody will make an ASIC to mine it for profit.
You can bet your ass on that. Conversely, it could be said that an ASIC-proof coin is a worthless coin.
If a lot of money flows into making ASICs for a specific coin, I'd suppose that the market around that coin at least provided some potential. Litecoin is showing us the opposite at the moment, I guess...