It would be nice to grab pieces of a many-valued property in service links. For example, a document with a Property:Version composed of filename + revision number could link to the right version in a VCS.
But it seems many-valued properties don't implement getServiceLinkParams(), so even if you specify [[Provides service::xyz]], no service link shows up.
The simplest approach might be for SMW_DV_NAry.php to invoke getServiceLinkParams() for each element. That file notes " * TODO: support outputformat", maybe that's the same as this bug.