Default and named datasets in federated queries

Hello

When reading the grammar rules for federated queries [60], I cannot see a way to specify default and/or named datasets in the federated query:
http://www.w3.org/TR/sparql11-query/#sparqlGrammar

Cannot see it here either:
http://www.w3.org/TR/sparql11-federated-query/

Nor in this document (where the rule is now [59]):
http://www.w3.org/2009/sparql/docs/query-1.1/rq25.xml#sparqlGrammar

As it is today, they only reasonable interpretation I can see is to make the federated query against any default datasets defined by the remote server. Is this correctly understood?

The other possibility, which I see as not particularly suitable, is to send the default and named datasets defined by the main query. This could however cause a lot of problems. Say the main query uses a series of datasets which it fetches (or holds internally), and are only used by the main query. Sending these to the remote server, could cause that server to load the datasets from the first, since it might not know if they're useful or not.

Is this issue discussed/solved already? I.e. Is there a coming solution where you can specify default and named datasets in federated queries?

Sincerely,
Peter Waher