BJ, I think the reason many of us have shifted to this being Stallone's to lose, in spite of his performance in the biggies like BAFTA and SAG, is that the reception he's gotten from the industry with his win at the Globes. It was loud, visceral and clearly enthusiastic.
The thing we have to realize from the SAG perspective is that they've gone to a situation where a small committee does the nominating rather than the entire organization. It's the reason an acclaimed indie like Room would be skipped over at the Spirit Awards. A small voting pool selecting a narrow set of nominees. Had SAG been selected by the body at large, I have no doubt that Stallone would have been nominated and would likely have also won.
He's also a very American institution, which is the reason I think BAFTA left him off. As BAFTA has proven over the years, they lean towards honoring hometown folk with nominations, and sometimes, wins. While the Academy may seem like a more global entity in terms of its membership, I think the nomination of Jennifer Lawrence, pretty much solidifies any perception that they are heavily Amero-centric.
Why does a win for Stallone seem like a more likely thing than one by Eddie Murphy or, more recently the comeback king Mickey Rourke (or even Michael Keaton for that matter) is that unlike those figures, Stallone has prior nominations. Two of them actually. I don't know whether Stallone survives Creed as I haven't seen it (nor do I really want to watch it, my affection for Rocky being quite weak), but he has the kind of emotional story backbone that, unlike Keaton and Murphy, tends to get people's attention.
Rourke was never an industry figure, just a popular actor who fell to drugs. Stallone, on the other hand, has apparently been well liked in the industry for awhile. Add in the nostalgia for his Best Picture winner (which still mystifies me, by the way...it isn't that great a movie), gives him a better shot than those three actors mentioned.
Lauren Bacall is probably the best analogy that I've heard so far. She was previously nominated and was a towering figure in film history. However, was she really that likable? That, I think, might be the key to this race. Was Bacall the easiest person to get along with. Her character in The Mirror Has Two Faces was also entirely unsympathetic. She wasn't a scenery-chewing villain like Christoph Waltz, but her character also wasn't the mentoring, sympathetic figure Stallone's is in Creed. Did Bacall even campaign much for her Supporting Actress category? I don't recall, but Stallone is schmoozing like there's no tomorrow.
I think all these factors combined lead towards a more likely victory for Stallone than anyone else.
"Any society that would give up a little liberty to gain a little security will deserve neither and lose both." - Benjamin Franklin