I was bullish on Sanders at the start, but I don't see it at this point. My thinking was that he could be the kind of Palmeiro/Trump candidate--in a big field, anyone with a decent bloc of support can win. But given that high recognition, the fact that he hasn't jumped out to an early lead in polling now looks like it's just that voters don't want him. I think I overstated his base, in part because of the media narrative of the race (which, note, he lost by 12 points and much of his support was likely coming from anyone who wasn't happy with the nominee, regardless of how much they supported him as an individual). Early polling is looking really good for Biden, but I suspect that will go way down if he actually starts campaigning (he's run before and never done too well, and I could be biased here because I'm not a fan, but I think exposure will be bad for him).
Harris is looking like she has a shot, but there are also some subsets that are strongly opposed to her. I think she'll do increasingly worse as the field thins. I think O'Rourke and Klobuchar have shots. Beto really inspired the base nationally and did exceptionally well relative to his electorate lean. Klobuchar has consistently done well by that measure. I also think it would be underestimating the field to say that only six people (I see Brown and Warren being strong, too) have a chance. Good chance that someone unexpected slips in there.
Generally, I think it's inherently unpredictable because unforeseeable future events will have a large impact on the shape of the race. And aside from it being difficult for a serious, informed, intelligent analyst to predict, most people just spout off ignorantly and let their own bias guide their "analysis" ("candidate I dislike will surely lose unless the media is biased," "candidate I like will win unless he gets screwed," or some shit).