Out of interest, are there any thoughts as to how templates are likely to access Commons Wikibase ?
I could image Commons Wikibase sharing the same Properties (Pxxx) but having its own items -- perhaps starting C (Cnnnn).
Such a structure would make it easy to prototype templates using items on Wikidata while Commons Wikibase was being developed, just changing the relevant Q-numbers to C-numbers to port from accessing an item defined on Wikidata to one defined on Commons Wikibase.
Properties on C-numbers could point to Q-numbers; but (with very rare exceptions) properties on Q-numbers would not point to C-numbers.
Is that likely to be how things will be set up?
-- James.