Hi Christophe,
In 1.5 the vdc.storageCapacity works. In 5.1 doesn't work anymore because the new Storage Profiles, but none in the Rest Api is the information of use of this Storage Profiles.
I will give a try to the Query Service. If you say that vCloud console use it in order to show info then must be there.
I'm downloading the PDF to investigate.
Meantime, I thing vmware should try to add this information to the Rest Api and the plugin.
I let you know if I find something in the query service.
Thanks a lot.
Damián