Thanks for the feedback.
As I see this idea operating, any new identity would have an average hash rate of zero to begin with (say the protocol assumes a new identity has hashed at 0H/s for the infinite past), which would mean that starting a new "identity" results in a penalty on any hash rate attributed to that identity. This means that the economic incentive is to stay using the identity you already have.
While I do appreciate what xenumonero does for the Monero community a lot, I do have some reservations about this method of defending. Renting hash rate works for an attacker because it pulls the hash rate towards their pool. But how much of the hash rate this fund rents was not already mining Monero? If I had a miner out for rent it would be mining all the time if not for someone else, then for me.
Do we have any stats that can show what percentage of the rented hash rate actually increases the network hash rate?