The people I suspect the most are Wei Dai, Adam Back, Nick Szabo, Ian Goldberg, or a few people of that era. Look at people who did interesting stuff then stopped for a few years... (Zooko, Jim McCoy, some Dutch people, Ian Grigg, etc are all candidates too)
I think we can rule out Zooko. I've been reading his stuff and interacting with him for a while, and between his personal life and Tahoe-LAFS, I simply don't think he had the time; and his delayed reactions to Bitcoin are not at all what I would expect from the creator. He and Satoshi simply sound different.
If Zooko has had challenges in his personal life over the past half-decade, Hal's had even huger challenges! IIRC, Nakamoto was active well after Finney announced his ALS diagnosis (October 2009). Also worth noting is that Finney was an active participant in the first email thread started by Nakamoto announcing Bitcoin, and seemed relatively hostile (I suppose Finney could have been arguing with himself, but you'll agree that it makes the hypothesis a little less likely).
