The protocol provides no way to send a scrollback or a history of messages. Additionally messages have no timestamp, so you don't know when they were written, only when you received them.
How it actually accomplishes that within the framework of the "protocol," I don't know.
The Quassel protocol supports this, unfortunately it looks like the quassel team doesn't care about taking it further than where it is.
Senders – there's absolutely no reason to fake senders, since it was always valid for messages to come from people not in the channel.
In a future release InspIRCd will adopt support for the server-time extension which will allow us to get rid of the timestamp duplication if a user's client supports it.