I have succesfully used it on live and PTS.
It is case-sensitive and must be written as Chip said: $(APIVersion)
not $(apiversion) or $(ApiVersion)
As you still have to increase the APIVersion in the manifest (and upload a newer addon) after the update goes live, the only scenario I have found is: Creating an intermediate version addon, which does not scramble saved variables due to breaking changes, if the user allows to run "out-dated" addons.
Another drawback compared to GetAPIVersion() is: You can not say APIVersion>=100012, only APIVersion==100012. So again, once the update goes live, you need to upload a new version, which removes the version substitute again, in hope the next API version will not affect your addon, again.
But migration is definitely better as without the substitute.
Thank You, Chip!