Any premine nowadays is an awful idea. 51% attack is not a solution, since the value needed to take over the network was slightly increased by 20%. Which means you have nothing against 71% attack. Moreover, the coin has nothing new to offer.
It actually requires about 40% more resources to perform a 71% attack as opposed to a 51% attack. I agree that for someone who can get 51% of the hash rate, getting 71% instead probably isn't nearly as difficult as, say, someone getting from 1% to 21%. But I have a difficult time seeing how this increase in the threshold is completely without value.