The problem is, that when it become inprofitable -- miners would shut down their ASICs and wait for better time -- causing difficulty to drop. And at this poin

The problem is, that when it become inprofitable -- miners would shut down their ASICs and wait for better time -- causing difficulty to drop. And at this point somebody with huge computing power disabled could enable theirs Rig and quickly generating block to perform double-spend, and create soft fork.