Description of problem: As mention in Bug #1361617 , could be useful query src.rpm by Exclusivearch, also add query by ExcludeArch can be complementary TBH I don't remember why and when I needed this ...
I agree this is a useful feature. Pungi (a compose tool used by rel-eng) would use this information as well in order to do noarch filtering when Exclude/ExclusiveArch is set. Unfortunately the information is not in repodata. It requires changes across multiple tools. I'll keep this bug open to be worked on in the future.
It looks like that the feature cannot be implemented because required information is not present in metadata. Repoquery depends on information present in metadata therefore closing the issue.