I would anticipate that pools/ miners will actively scan pending transactions. Which leads me to the thought that they might shutdown to save power when pending transactions don't contain enough bitcoin to profit on, opening a vector for attack as it artificially decreases the difficulty
I'm not sure what you mean by "actively scan".
Petertodd suggests that people should be nlocktiming some of their transactions for the future to reduce problems with this. E.g. once the current block has enough incentive, start making transactions that can only be mined in the one after it... Regardless, if transaction load isn't so high that blocks are mostly pretty full, I suspect we'll have much greater problems than miners running intermittently.
