Group iMessage = CC list, cc list becomes messaging group. I suppose one way this could play out would be simply to add an email submission API for text messaging app(s), but it's an incomplete idea so far. :)
I'm still not sure what you mean. Are you simply talking about an email client that looks like a text messaging program?
I like that idea; An email client that looks and behaves like the regular messaging apps in iOS/Android.
That's doable. The image in my mind was the reverse: a chat program that displays email threads. Interactions in chat become mailing list replies emailed out, and replies to the CC list are displayed in the chat channel.