I'm just going to say it. Ellen CANNOT be the 5th. I refuse to believe it. Why would R. Moore bestow such a significant title to such an insignificant character (who isnt even a main cast member)?? The other four were ALL major characters (well, maybe except for Tori)
Starbuck might be the fifth....maybe. She's a big enough character to be the fifth. But....for some reason...I also doubt this. The Final Cyclon has to be someone IMPORTANT (either Admiral Adama, the President, or Baltar). The entire series has been building up to the revelation of the fifth cyclon. I don't think Moore would waste it on being 'starbuck' or even 'apollo.'
...Or Moore might just do a complete mindfrack and have it so that it happens to be that EVERYONE's actually a cylon. But that's just a theory....
It's not actually a bad choice. I didn't expect it to be one of the main cast anyways. Too many of them are already cylons. At least it was a major recurring character. And I think that to make any of the other main characters cylons would compromise their humanity.
That has always been the thing about this show. The people are so completely flawed and human, that making them cylons would just almost give them a reason for being messed up. As in "they're messed up because they are cylons, not because they are human"
I even thought that Tigh was a bit much as a cylon. Same with Kara as a "goddess" or whatever she really is. Those were the two most messed up characters on the show and it kind of excuses them for being screwed up almost.
Of course, I know that they wanted a huge shock at the end of third season, and Tigh is someone that very few people suspected. And, the way they are going with cylons this season, being one of the final five might end up not compromising humanity at all.
But it could not have been Adama or Roslin. They are the parents of humanity (coloniality? I'm starting to think that humanity can't really be used to describe the colonials any more. The cylons could easily be just as human.) It's kind of like how Baltar couldn't be a cylon. He is the father of the hybrid race, Caprica is the mother. One cylon, one colonial.