It's getting more and more difficult to watch Battlestar Galactica. It really is. I just don't do well with dramatic shows that simply have no real hope. Or with characters that have collectively lost their way. The path this show travels continues to get darker and darker, and if it doesn't end this year with a great satisfaction, I'm going to be rather upset. And I'll probably feel, as I did to a certain extent with Babylon 5 and Farscape, that I've wasted some of my time being faithful to a show that wasn't faithful back to me.
I have higher hopes for Lost. But we'll see.
Anyway, about Galactica. Here are my two alternate ending theories. I don't think both could happen, though I suppose it's possible. I just think either of these revelations might occur.
1) A frequent phrase used by the human-looking Cylon skinjobs is, "All of this has happened before, and all of it will happen again." We've seen old-series-style Basestars, centurions and Raiders, as well as old series Vipers that were all supposedly used in the original war with the Cylons. I wouldn't be surprised if somehow the old series is tied back into the new one, as having actually happened before in the past. Or some alternate reality/dimension/whatever. That one time there was another Adama, another Apollo, a male Starbuck, a black male Boomer, etc. And as time went on and evolved, the current Galactica crew evolved into the current story we watch today.
2) The 12 Colonies were established by survivors/refugees of the planet Kobol, which was rendered uninhabitable sometime in the distant past - that much is established. Legend tells them that a fabled 13th tribe went off and founded the lost colony of "Earth". I'm thinking that last colony didn't go off into the dark, but went in search of the actual origin of mankind. That they probably found Earth - but didn't "found" it so to say. They probably resettled it, or established themselves into its own culture.
In other words, long, longer ago than even Colonial history claims, our Earth sent out travelers into the deep, taking with them the names of the Greek gods, the idea of monotheism, phrases like "We the People", the term "nihilism", toasters, neckties, automobiles, nuclear bombs and, yes, "All Along the Waterfront" by Bob Dylan. These travelers from our future eventually settled Kobol, established themselves as an original settlement, long enough to reclaim the Greek gods as their own theology, then eventually founded the 12 Colonies. One group decided to hike back to Earth and see what was up. What happened to them we'll probably eventually find out.
And this is more likely the origin of the "All this has happened before, all will happen again" motif.
Whether the two theories merge, and the old-series BSG crew is really the original returnees, I don't know. But I wouldn't be surprised to see both ideas incorporated into the ending.