Hi Ry, I did read your posts and this thread several times. I'm just stating that I agree with the original poster and with Brent. I have not come up with any a solution using Messages that allows anyone to see texts from my Google Voice number.
My GV number is the one that I too hand out to all to use. I have filters on my GV account for my business calls to go to one voicemail and my Starred Google Contacts to another even though everyone calls the same number to reach me. I also have it set up so if someone is not in my Starred Google Contacts, my cell phone does not ring so I am not bothered by anyone outside of my business hours outside of those Starred Contacts.
The Google Messages app I would LOVE to use if it could only be enabled to show only my GV number to anyone I message (I truly don't care if it's text, SMS, or RCS). I would just like to have a single solution again as Hangouts was previously.
I had everything routing through Hangouts, calling, texting, messaging/voicemails and when the SMS integration was pulled last year, I held on as long as I could. Even enduring the message that was always at the top saying Hangouts was no longer integrated and I needed to download another default app for SMS.
My Galaxy S4 phone died in December (I gave that device such a good run) and the Moto G5 Plus that I replaced it with is fine and came with Messages as the default 'texting' app (read:cannot be uninstalled). Again though, as I couldn't get Messages to send out showing everyone my GV number, I wound up installing Hangouts and GV again and was having multiple apps to do what is really one function to most of us - reach out to people via texting. The updated GV app is so much nicer to use and I recently went back to Hangouts in full once it re-integrated with GV and allowed me to have everything in one place.
The update to Messages this past week is nice and I would enjoy being able to use it for all. I have Allo for my best friend who uses it because she loves the silliness of it. Hangouts for my parents who don't keep their phones turned on but who have the Hangouts extension on their browser so that they can message me wherever I am. GV for everyone else: co-workers, family, friends.
I hope that helps explain it better. Not that I expect you to solve the Google messaging platform, I am just chiming in that I dearly hope Messages will one day be able to show to anyone I send a 'text' to, my GV number only.