We all have an Apple ID. iMessage associated email addresses and phone numbers should sync around it. Let’s get rid of per-device settings. They just confuse everyone. The vast majority of us don’t need that much granularity.
He’s got a great list of suggestions, but I must be alone in the fact that I don’t seem to have issues with message histories. I will say: it’s stupid that iMessage doesn’t revolve around just one ID.