Keccak is SHA3..
which will totally kill off ASICs of todays current design.. and would cause the system to take weeks to solve one block because the difficulty is soo high, by the time that 2016 blocks are solved (years) to then downgrade difficulty, would be too late...
Yes, it will kill off today's ASICS. But I disagree about the difficulty. Obviously the hardfork would not only change the PoW but initialize the difficulty to a reasonable value for that PoW.
and in 3 months-1 year china will have SHA3 asics and dominate again without 6 years of difficulty growth because the difficulty has been reset, so although you might has mentioned the difficulty may change to not cause transaction delays for users.. its still not solving the dominance issue, long term
plus ofcourse if the difficulty did drop to a level that an average laptop can solve in 10 minutes.. then nefarious users will syndicate(group/pool) multiple systems together to 51% attack very easily and cheaply