So to be honest I see that article (linked below) and I think "Yeah that's probably all right", but given this is for a Real Sytem With Serious People's Data, when faced with "take the downtime and do the offline data upgrade that _basically everyone does_" and "try to use logical replication to get a new database in the right state, knowing that logical replication doesn't copy _everything_ so I need to manually copy some stuff, and if I miss stuff I'm in a bad situation"...

I trust the pg people that tools do what are advertised, but it's a very high risk proposition