Hi!
How about adding an ODbL licensed service? Would it be possible? I am thinking about SPOI http://sdi4apps.eu/spoi/ and their SPARQL endpoint http://data.plan4all.eu/sparql..
ODBL seems to be in the same vein as CC-BY-SA, so if CC-BY is ok, that should be OK too. Please add the descriptions to https://www.wikidata.org/wiki/Wikidata:SPARQL_federation_input