-1   I don't think this is worth the semantic change.  The current 
approach doesn't require special cases for different dict sizes. The 
code/time savings is very small (seven bytes of opcodes per item get 
condensed by only one byte and the cost of one time around the eval-
loop is tiny in comparison to the cost of inserting a new dict entry).  
Besides, dict literals almost never occur in the inner-loops of time 
critical code. 

I recommend that this stay closed.  Better to aim for meaningful 
optimizations using the AST and avoid micro-optimizations that subtly 
change semantics.