We had concerns on implementing glance storage location strategies in Nova. A counter-proposal was made to only pass the original image ID when calling Glance for a snapshot so then Glance would then use any store the operator wants (eg. a location strategy like "please store the snapshot to a place close to where the original image is").
The agreement was there for the counter-proposal so the Nova change would only be to pass the original glance image ID to the new glanceclient that would support it. Glance folks will provide a new spec revision.
-S