not a sound investment proposition 
as you cannot even make a "gentlemen's agreement" for a criminal activity...
it's true however many PoW coins don't have the hashpower to withstand a serious 51% attack, they might benefit greatly from modifying their blockchains with the newer and more robust proof methods.
Like the sign says, "If the cash is there, we don't care." as you cannot even make a "gentlemen's agreement" for a criminal activity... it's true however many PoW coins don't have the hashpower to withstand a serious 51% attack, they might benefit greatly from modifying their blockchains with the newer and more robust proof methods.