I've heard the rumors about Nexus 2 by Motorola a while ago , even
before the Nexus S came out , but i think Google went with Samsung because it was cheaper for them (No R&D cost) , its just anther variant of the Galaxy S (with small differences here & there) more like the I9000 , Epic , Vibrant ...
it even have the same S
if the next Nexus is built by Motorola , I don't think it will have the docking features like the Atrix , since that will require Motorola to put some extra stuff which will be the opposite of Pure Google phone (not just a MOTO phone portal like the Droid\MileStone)
Honestly , I don't like the looks of a Vanilla\Stock Android & I prefer a custom UI on top of it (MotoBlur or Sense) even though i'll end up using a custom launcher
at the end , every one have his own taste\opinion & that is just mine