FWIW, I'm -1 on the proposal because it partially overlaps the existing
capability of dict.update().  To the extent it doesn't overlap, it is
use case challenged (typically, it doesn't make sense to build a
brand-new dictionary from two independent dictionaries and the atypical
case easily fulfilled by a couple of updates on an empty dict).  

Also, the notation itself is at odds with the existing pipe-operator
used by sets and by dict views.

FWIW, there are other alternatives to directly combining dictionaries. 
See http://code.activestate.com/recipes/305268/ for one example.