Well, FreeFrom team. In FreeFrom, a user can upload 9 pictures at once without waiting. I wrote a in-app fake relay (local) to handle the pending event which contains still uploading resource URIs. The sender will see this event be published and rendered immediately. Now I am planning to extend this relay to store history events.
Of course, this in-app relay may be different than the local relay you mentioned. But I think the idea is the same. Maybe I am wrong