Tag/Group editor sufficient for some cases.
Metacontact XEP vs vcard4 XEP for storage.
Unified conversation history, but make it clear what message went from/to non-primary JID. Allow choosing which to send to right now? VS no unified history, select alt JID from contact details page to open alt conversation.
Contact Details page show all JIDs
Two JID one contact ALSO one JID two accounts?