Yea, I thought about this a while back. I think, all iMessage is routed through an AppleID (and I assume that's how apple is by passing the text message system). So assuming all iPhone users has an AppleID, and all iMessages are routed via AppleID then I don't think you would have problem getting all the "iMessages" to sync on your iPhone, iPad etc... However, I don't think you are going to be able to get those text message (via phone number) sync to your advices other then (iPhone).
I guess I could see that been a potential problem, but then again it depends, my fiancé, most relative and friends has an iPhone so I guess it won't be much issue for me. But yes I can see your concern.