Bitcoin could hard-fork to a memory-hard algorithm (like Lyra2RE), or even change to any hashing algorithm for which ASICs don't exist yet. Even if they switch

Bitcoin could hard-fork to a memory-hard algorithm (like Lyra2RE), or even change to any hashing algorithm for which ASICs don't exist yet. Even if they switched to Scrypt (from SHA256) for which dedicated hardware exist, it would cost them millions of dollars and require months of manufacturing re-organization to get to their share of hashrate. Of course, the miners would still be able to mine the old fork and at that point it is more likely that an altcoin (like Ethereum, Litecoin or Vertcoin) would eat up Bitcoin's marketshare.