I've been struggling to understand what should go into wikidata and what should not.  I see that this is because it hasn't been decided yet ;)
http://www.wikidata.org/wiki/Wikidata_talk:Notability

In helping the community to make this decision I think it would be really helpful for the developers to weigh in on the technical capacity of the envisioned/realized wikidata infrastructure.  If we know how big the system could realistically be and continue to work well technically, it might help discussions about how much and what kind of content we should put into it.  If the plan is to cope with only a few tens of millions of subjects that is quite different than if the plan allows for the potential creation of billions of items.  (Suggesting less inclusive versus more inclusive policies).  

?

-Ben