> It's been around a long time and bitcoin hasn't been changed to take advantage of it.

Of course it hasn't, Bitcoin is decentralized and Peercoin requires the developer of the system to continually sign the chain.

Proof of stake sounds lovely, but it doesn't work and attempts to rescue it have at best resulted in things with very different security assumptions and properties from Bitcoin. https://download.wpsoftware.net/bitcoin/pos.pdf