There is no way to query existing publicly exposed data on users themselves.
A lot of users use the User_Info template and include data items (like IRC, image, full name, languages spoken, etc.). This data is already included on their User profile page and ought to be available through wikibase.
For instance Q23034479 has a a property P553 which has a value "Wikimedia project" and a scalar value of User:Katherine (WMF).
It would be helpful (I think) if publicly exposed properties (that are already on the User page) could be added to a item of User:Katherine (WMF).
- Query all of the users who speak at least level 3 Spanish.
- Query all of the users who have a picture.
- Query all of the users who have an IRC nick
Users should automatically become wikibase items in their own U namespace.
To do this we will need to enable wikibase on Meta and create a U namespace that can be distinguished from the existing main Q namespace on Wikidata. The Id of the user should be the same as the CentralAuth id.
For instance, my central auth id is 50584396 (as reported by the API), so my wikibase ID on Meta would be U50584396
This would also allow me to reference the property on my user page (just like referencing a wikidata property on an article).