Please correct me if I'm wrong, but doesn't PoS require the miners to keep their private keys online on the machine doing block validation?
NXT allows you to lease the balance of your account to another account for forging. This way you can lease your balance to an empty proxy account that can remain unlocked/online without any risk. If the account is compromised, you simply issue a new lease transaction for a new account, or move the coins out of the leasing account. A lease only becomes effective after 1440 blocks to prevent a number of exploits that would otherwise be possible.
http://wiki.nxtcrypto.org/wiki/Nxt_API#Lease_Balance