Are democrats actually considering swapping out Joe Biden for another candidate?
Oh god, I hope not. Hillary had her chance, she blew it. People who lay money down on things like this, for the most part, aren't retarded, and the contrarians are factoring in certain elements I can only speculate upon. But I would say the 84% for Biden seems pretty accurate. The only other option I would consider betting on would be "Other". Betting on Hillary seems like a wasted dollar, but what do I know.
Highly doubt they're going to do something like that, and I doubt that Biden would willingly step away and that's really the only way to be able to do this without a civil war in the democrat party. I know I've said it time and time again, and its still true -- Biden doesn't have energetic supporters backing him -- but replacing Biden at this stage (yes, even before the convention) is going to kill the party and make it look CRAZILY fixed.
Even if Clinton had the backing of the Democrat party, with fundraising and such, she did still win the vote totals and the amount of delegates needed to clinch the nomination.
If you brokered convention Biden (not even sure how this would happen) and replace him with a dark horse candidate like Clinton, Bloomberg, etc -- you're going to see the Democratic party go poof VERY quickly.