Would this be enough to cause people to switch en masse to this hypothetical new mining technology?
Considering most "miners" are people who are using equipment they already have, probably not. Dedicated miners, who knows? Probably?
I know that if an ASIC design came out that was fast and cheap enough, I might buy into it, but it'd have to be my view of fast and cheap enough. I don't have cards dedicated just to mining, they also serve the purpose of LAN gaming. But I have interest in BTC, so back to the first sentence...
In December and January I spent money on a bunch of 5870s. I also paid for some heavy power supplies. I already had mainboards and CPUs to run them. The resulting cluster runs 9 5870s and has mined a reasonable number of Bitcoins -- the outlay has been covered and profit has been made.
The increasing difficulty means that the rate of Bitcoin mining is slowing down - I currently expect to mine a block about every 30 hours. The 50 Bitcoins are worth roughly £22.8. The power used costs roughly £6 so each block makes a profit of about £16.8.
Difficulty tends to rise in steps of about 40%, so the time taken and power used to mine a block can be expected to rise to 42 hours+£8.4 then 58.5 hours+£11.76, 82.3 hours+£16.46, 115 hours+£23.05.
So, after 4 difficulty increments, assuming we see 40% increases each time, it will no longer be worth the cost in power for me to mine Bitcoins at their current value using the 5870s. Of course, as the expected return on investment in GPUs becomes smaller, we might expect that less people will be investing in mining hardware -- the difficulty might not actually increase so rapidly.
There may be an opportunity for someone to offer me and other miners a technology that can mine Bitcoins at a lower cost in power. Of course, whatever technology that turns out to be will have to have a low enough initial outlay that I would expect to be able to recover it in a reasonable amount of time, such expectations would be influenced by the knowledge that lots of people are likely to be buying and using the same new technology.
ASICs are expensive for small quantities, cheap for large. But how many SHA256 ASICs would one expect to be able to sell? And how much performance per Watt can actually be achieved?