Duo already has multiuser (8 or 12 max) support. It's intended to be a competitor to FaceTime. Meet is intended to be a competitor to Zoom. They're not getting combined anytime soon, even if Hangouts is going to die.
Nah, it's not popular. They'll wait until someone is actually using Duo before announcing its sudden demise. They'll probably open up an API first to make it all the more painful.