Any ASIC is vulnerable to changes in Bitcoin. (Including BFL)
Should any changes occur, the losses could be staggering. Those with FPGA's ought to keep them as insurance. Especially in light of the GPU miner shutting down once ASICs dominate the market.
How and from whom could such a change be done ? is there any kind of "consortium" who decides which algorythm is used ?
Any change in the bitcoin code will create a new fork, which will no longer be the the original "Bitcoin".
So while you COULD change the code, none of your new coins will work on the original Bitcoin platform, where all the ASICs are.
Maybe not? let's say change is from sha256(sha256(x)) to sha256(sha512(x)) and change will be implemented at block number Z. All old transaction (recorded in blocks older than Z) will be verified with old algorithm. All newer will be verified with new algorithm.
But I doubt such change will occur. ASICs are a necessity for bitcoin network to make it less vulnerable to a malicious entity, even if it will mean small miners will be taken out of the mining party.
LOL you must be new....
For a fork to work, the miner must support it. If more than 50% of miners are ASIC, you should forget about new fork.
I'm glad I made you laugh
But I was saying that a fork with a new hash function can be made and coins mined before Z-day can still work on the fork. The transactions are made (and signed with a hash) by the clients, not the miners. So even if ASICs have >50% hash power, the clients which agree to the hash fork will be able to use old coins. If something is wrong with me reasoning, I'd appreciate you'd tell me.
Indeed such change would create a mess, like SgtSpike said, and also because pre-Z-day coins are valid and can be double spent by clients on both ASIC and forked chains. So, as you said, such a fork (without consensus) cannot work and will not appear.
But a hash function change which is agreed by community (for example because a sudden sha256 flaw is discovered) can be made, old coins will be valid, and it will render the old ASICs useless.