Others have mentioned it as well, but telegram had this implemented at the same time this was written. https://telegram.org/blog/bot-revolution
They only lack the user base.
I would also like to see this functionality in all messengers to offer the chat to anyone, not just Apple users (even though iMessage protocol was to be open).
The other point I’m concerned about is verifying the validity of the sender. If it’s mixed in with SMS how is the end user to know it’s not someone or some thing maliciously trying to socially hack information? I don’t doubt there will be a solution, but it’s training users to trust anything.