This attack shows how using a myriad of AuXPoW chains could avoid this problem.  As by using a myriad of chains then the attacker would need to attack more than one chain.  While using AuxPoW with the biggest coin on each chain would greatly increase the network hashrate.  I think you should quickly adopt AuxPoW with litecoin how Dogecoin has just done so to help stop any potential future attacks.  Then the myriad with NeoScrypt Feathercoin merge-mining and Lyra2 Vertcoin merged-mining can brought in a later date.  Plus it may be worth including Cryptonight Monero AuxPoW with the myriad.  Plus possibly X11 Darkcoin merge-mining included in the Myriad.  To have a total of three to up to possibly five myriad chains all in AuxPoW with the biggest networked coin on each chain.  As with a myriad of five chains then an attacker would need to control three of the five AuxPoW chains to control the network.