Good revisions so far.
More suggestions:
1) How about mentioning bittorrent instead of hashcash? Bittorrent is a huge buzz word and could grab some attention. As a completely distributed and anonymous network, I'd say that Bitcoin is similar enough to justify the comparison.
2) "...clients burn CPU cycles..." --> "...nodes burn CPU cycles..."
3) Throw in "decentralized" and "proof-of-work based" somewhere
4) Personally, I'm still not fully satisfied with the mention of energy-backing. Maybe you could replace it with something about the time-stamped transaction history being voted on secured by the majority of CPU power?
5) Not to be a smartass, but watch out for passive voice (e.g. "It is expected that over time..."). Headlines and news articles usually try to grab readers' attention by using the more exciting active voice.
Feel free to take all, none, or somewhere in between. We're critical because we care
