For some reason any of my users don’t see that under rebuilding. Well, on chat anyway and that’s why there has been some incidents where an user has lost just written message.
My opinion is that situation where we don’t inform at all downtime for already login users is the biggest single UX-issue in Discourse. Sure I can understand explanations where is comes from very nature of this app, and devs are kind of painted themselves at corner from the very beginning (similar situations like with drafts and few other things), but it doesn’t erase the problem itself.
We have few worksarounds. Using Nginx as reverse proxy fronf of Discourse showing tuned error page is one. And when an admin has problems the answer will be ”we support only standard one”. That was the actual reason why I dumped that one.
Two different containeirs is one solution. Or at least it keeps downtime very short. There is too many warnings on that, so I’m a bit scary taking that road.
Or we can upgrade only sometimes, inform users before it happends and shutdown public access. Yes, that is one solution, but… now is year 2024 and only banking system uses that in my environment 
Using staging server is something that should do. Well, that is corporate level solution, expensive and quite difficult way when done right, and loves own IT-team.
So new leaked plans 
are real improvement indeed. Well, if it needs separate containers then there is time to dive in at the deep end I suppose.