TBH I think keeping SMS separate from an ip based communications method is better. Lets not pretend that SMS is secure. The only thing I would find missing are quick reply APIs.
How are IP and SMS traffic different, other than "packet" size and encoding constraints? Both are easily interceptable and spoofable, necessitating strong crypto.
I don't see how chacha20/poly1305 is somehow "worse" over SMS.
The difference is mostly that in case of SMS, metadata leaks to carriers. In case of Signal/TextSecure/RedPhone, some limited metadata leaks to Google Cloud Messaging and Apple's equivalent platform (I can't remember the name). That's necessary because of scaling problems with push messages, but I understand there is work going on to develop a self contained alternative using WebSockets.
