They should have announced it in February if they were going to change the VP slot on the ticket. It wouldn't look like desperation that way. As it is, if they jettison Biden it looks like a desperate move of a campaign with no clear notion of what it wants to do and where it wants to go.

We all know the vice presidency isn't worth a bucket of warm piss, and I also highly suspect that the Clintons still hate Obama with a passion and will actually undermine the administration in subtle ways between now and November. As such, I'd be more likely to see the Obama team ready to swap out the Gaffemaster only to have Hillary say something along the lines of "if nominated I will not run, if elected I will not serve" than to see her willingly take up the least valuable spot in a second Obama administration.