That is my take on it also.
If the Republicans try to spring Yeb, Rubio, or Kaisch on us - they need to go the way of the Whigs (or Dodo birds).
I think the pros look at it like this: Carson and Christie can't make it. Fiorina is already out. They will (somehow) destroy Cruz and Trump. Or, Trump will do the job for them (destroy Cruz and then himself). Maybe they figure Trump destroying Cruz IS destroying himself.
So that leaves an untested and absurdly ambitious Rubio (R-Foam Party), Kasich, and Bush.
Of the two governors (it has to be a governor, right?), Bush governed more conservatively, so, that's it, then.
I think FR is going to get its Trump-Cruz ticket, but not on the GOP line. And I think the netroots will get their Sanders-Warren ticket, but not on the Democrat line. The Republican ticket will be Bush-Kasich, the Democrats will be Biden-Castro or Biden-Patrick.
Hillary's going to prison.