So, the news has broken, SaveCarsonBeckett.com did it!. I'm still wary in the way of I'll believe it when I see it, i.e. when scenes have been filmed and there's been no scheduling/whatever problems to excuse lack of it or anything else that could legitimately interfere with the successful upholding of JM's part of the deal. That said, yay!
I am, however, now wanting to figure out what the back end of S3 clue is. Something relating to Michael perhaps? Something major missed or a consequence of the strangeness at the end of First Strike? (maybe they jumped in time with Atlantis and not just space - making it not Carson who's time travelling but the whole of Atlantis)
There's also the slightly disturbing fact that JM promised to bring Carson Beckett back - the character - and I see no indication specifically about Paul McGillion being back for the role... EDIT: This GW article seems to confirm it will be Paul! Making it not Carson in someone's head nor played by another actor. So how? Might be possible we'll get an ascended Carson, if that would count as in the flesh, RepliCarson or genetically cloned Carson by Michael's experimentation like say, a wraithed!Carson or hybridised in some manner as payback for Michael's own state.
Saying it's not AU or timetravelling Carson still leaves a lot of alternates open.