Are there any other purposes for this coin apart from being airdrop at the moment? So far I think it's only for minting yes?
"PoSToken is just a start of Proof-of-Stake tokens and the PoSTokenStandard will help developers issue more PoS tokens in the future. That's the real purpose of PoSToken. We believe that a new era of Crypto Tokens starts here"
Quote that you find easily at first page

Yes, proof od stake tokens can be a breakout technology, I guess many tokens will adopt it in future. Actually I am planning myself a currency right now that I think could benefit introducing this technology in future

For the moment, we find that a few tokens follow the PoSTokenStandard, such as EtherPower, Accelerator. We believe that more and more tokens will follow the PoSTokenStandard in the near future.