One thing to consider is weak etags. No self respecting blob store should return a weak etag; but if it does I suspect the /graceful/ production behavior here is to skip the leading /W of the header and continue as if it were a strong etag. 

In a /live/ test it may be useful to check new implementations (possibly a poor-persons blob store backed by tomcat) actually return a weak etag and fail the test until someone figures out why that blob store does not respect itself.