I have no particular issues with the change, but the commit log doesn't
tell us why this is needed. Was something breaking ? is there any risk
to the assumptions that other classes/recipes/layers may have made
about the location of the unpacked files ?
The go-vendor class was unpacking dependencies to ${UNPACKDIR}/git
and then needed S = "${UNPACKDIR}/git" to find the dependencies. 
Changing the S variable caused the do_qa_unpack() from insane.bbclass
to throw an error.
 
There shouldn't be any other assumptions from other classes/recipes/layers
that have been broken. The recipes I tested this change against used sources
fetched using the go_src_uri() function, regular git fetching, and local files.
There weren't any issues with moving to the go dependencies to the new
location. As far as I know nothing in openembedded-core uses the go-vendor
class making it trickier to test against a known baseline.
 
John