If my tests are not mistaken taking out the ObjectType from the xAOD namespace reduces the number of shared libraries .so actually loaded due to the dictionary for this enum.
Now there were a couple of issues since clients expect xAOD::Type:: while we now have xAODType.
aliasing the namespace should help basically expanding on a suggestion from @khoo.
Mentioning also @mhodgkin and @ssnyder
Then there are some additions on python loading the dict etc (many files but not many line changed), these can be also problematic , I guess the tests will let us know.