This is a completely flawed concept.

Let's say your PoM network has a total of 10ghash/s. In order for PoM to be making money though, they are only dedicating 1ghash/s to the midas network. And let's say an attacker has 2 ghash/s, so they have better than a 50% attack, they have a 100% attack and can make themselves the legitimate chain at will.

The attacker sends money to an exchange at block 1000 and cashes out to bitcoin/fiat. The attacker then uses his 2ghash/s to mint a blockchain twice as powerful as the legitimate 1ghash/s chain. He mines until block 2000, privately. He does not give any way for his double spending fork to be discovered. His chain is twice as powerful as the legit chain. So, now he broadcasts it. IT gets relatively instantly accepted as the legit chain. If the PoM pool kicked in and started using all 10ghash/s to bring the network back to legit status, it would not instantly flip back to legit status. It would take a series of hours or even days of mining to overcome the other chain. (about 10 times less time than the attacker took. So, if the attacker 2ghash/s mined blocks for 10 days, the legit chain with 10ghash/s would take 2 days to become more powerful). During this day, they could have their double spent coins go to another transaction and spend things again. Also, anyone else could do the same. Send coins to an exchange, cash out, then wait for the legit fork to undo that transaction.

The entire idea is one of the most terrible and ill thought out things I've heard in quite some time. I understand the intentions, but it's not possible. At all. It actually makes double spending significantly easier.