TaPoS (Transactions as Proof of Stake) is a system developed by Dan Larimer in 2014. Its most important feature is the inclusion of a recent block hash into transactions. I believe most of the developers here should know already about it (for those that don’t: here is the whitepaper - initially it was meant to be a “standalone” consensus mechanism, but current approaches use it as a complement to existing algorithms).
Its main advantage: if there is a fork, everybody can know which chain are following other Peercoin users. It is a bit like synced checkpointing, only that everybody can broadcast his/her own checkpoints and others can follow it.
I think the feature of TaPoS to include a recent block hash into transactions would be an interesting addition to Peercoin to mitigate the Nothing at Stake problem. If users, in presence of an “attack chain”, can simply follow the chain their peers use (e.g. their favourite exchanges or merchants) then an attack would become very difficult - the attacker would have to lure big and well-known nodes into his attack chain.
Some PoS and DPoS coins (NXT, Bitshares …) are already using this feature - can Peercoin add it, too? Was this discussed somewhere among the developers?
The only disadvantage I can imagine is that it would add some more bytes to transactions - but maybe the signed block hashes can be pruned at some moment?
(Edited for clarification).