Based on a similar mechanism with aivendbmigrate I would like to have major release upgrade mechanism based on logical replication.

Steps:

1. create an empty target instance with new major release
2. create a full logical replication setup (like aivendbmigrate does) 2.1. inform users about limitations (lobs, schema changes during that period etc.) 2.2. inform users about testing and rollback capabilities
3. perform the usual migrate thing with transferring everything and switch to a CDC state until next steps are defined
4. provide specific cutover scenarios 4.1. DNS switch if possible? 4.2. some pgbouncer magic to prevent forced reconnections of clients (maybe some prerequisitis necessary)
5. offering cutover in place or just to new instance

Benefits are
- in worst case downtime of the major release upgrade is just a "reconnect" away
- testing capabilities during the CDC phase to verify that everything is fine after the major upgrade
- if tests not successful a rollback is even not necessary
- after cutover the old DB could be conserved for some time to get back to at least the last state before the cutover as kind of a disaster recovery case.

The basics are IMHO already there in aivendbmigrate and even with the limitations of logical replication (which will be better with the next versions, and are better with pglogical) this would be a huge differentiator to other vendors, as this is best practices on premises but almost no cloud vendor offers similar solutions.