Sorry if this has been posted somewhere else, already, but I was just thinking . . . This human LeChuck, from his reaction to Guybrush's hand taking over to the way he acts towards Elaine (still affectionate, although in a much more sane way) shows a markedly different personality. What if "LeChuck" as we know him all this time was less the person and more the pox? Beardy could just be some nice bystander that got caught by it and hasn't had control of himself since. (He would've had to have contracted it while he was still alive, and then died later, according to the older games). Guybrush could "literally" be turning into LeChuck, if the curse/anger/pox is LeChuck and not beardy. It also makes more sense for the way the hand behaves, as well.
This could also explain the endscene (not the mystery person, sorry!) very well. Elaine has adjusted to the idea that this new person is not the actual LeChuck, but some newcomer she's getting to know. They've begun to bond over all of their experiences-- she possibly even thinks Guybrush is dead. He sees her looking down, knows she's thinking of Guybrush, and gives her a flower to cheer her up (or there's some strange plot twist where they've been searching for a flower in order to speak to manatees/merpeople and he's finally managed to get a hold of one and she's happy about that-- give the voodoo lady a flower if you're not sure what I'm talking about). She's willing to work with him, or cheered up by him, because she knows he's not the same person.
Don't get me wrong, I'm not 100% convinced of this myself, but my instincts as a writer (which have an eerily high percentage rate for guessing random but correct things) tells me this is a good direction. If you don't believe me give the game another playthrough. Watch beardies reactions very carefully. Watch when and how the hand reacts to things. I may not be entirely correct, but I tend to believe beardy is more a victim of the pox than the actual villain.
Anyway, what do you think? Discuss!