First, I did not realize the default SMS app would not work with plan 3.0. Otherwise, I would stay at 2.0 but too late, I switched (went with moto X pure). Next, I discovered that you do not need to use Google Messenger for your SMS. I downloaded Signal SMS app by Whisper Systems (whispersystems.org) and SMS/MMS seems to function fine.
I only tested with some of my contacts with wifi and w/out wifi for the past few days, so far no hiccup. If you value privacy and encrypted communications, give it a whirl and report/update this thread. No, I’m not affiliated with Whisper Systems. I figured more exposure leads to quicker bugs fix and adoption of encrypted SMS/MMS app, for free and without ads
(Telegram is another SMS/MMS app for individuals that value privacy. I have not try the app.)