Once again because this seems to be a reality that is misunderstood.
"Bitcoin" is by consensus the protocol as it exists today. You can fork that protocol but you can't force a change to that protocol.
That greatly limits the types of changes which will be accepted. Many people (myself included) never want to see a permanent split for any reason unless absolutely unavoidable. So if you (or the GPU miner's alliance) propose a fork (and yes ANY breaking change is a fork) that switches the hashing algorithm I (and many others) won't support it. A permanent fork would be massively disruptive, would destroy value, and would split the resources of the community. I would only change sides if I felt doing so would help to kill off one of the forks.
BTW I no longer mine and probably never will so this isn't some personal view to protect my own profit margins. It is just that having two "Bitcoins" each calling themselves "Bitcoin" and supported by a large group of people would be a worst case scenario. It is chaotic, will hamper adoption, and ultimately everyone losses.
It is highly unlikely (bordering on nearly impossible) that a core element of Bitcoin will be changed.
By a core element I mean things like:
1) Transactions are irreversible (even in cases of obvious fraud or theft)
2) Coins never "expire", there is no such thing as recycling coins (which is just another form of reversibility).
3) The network computes difficulty every 2016 blocks, has an expected time between blocks of 10 minutes.
4) Consensus in disputes (double spends) is enforced by a proof of work using the SHA-256 algorithm
5) There will never be more than 21M coins and the block subsidy schedule will be followed (50 BTC halving every 210K blocks)
The only scenarios I could see where a large enough consensus forms (among miners, bitcoin holders, merchants, developers, service providers, exchanges, etc) to change the hashing algorithm is either
a) Bitcoin is continually 51% attacked
b) a flaw in SHA-256 is found making preimage attacks possible
Essentially the network changes because not changing likely means a complete loss of all value and utility.
I hate to say it but you have described an excellent reason for a mass fork, so people can pick up cheap bitcoins...! this was sorta demonstrated as an effective way to lower btc price earlier this year