Specifically, it would be extremely useful to have:
(snip wishlist)
Are there any plans to introduce such functionality in the core PostgreSQL project in the future?
Getting failover to work, and work CORRECTLY[1], is an extremely complicated task, fraught with tons of complicated edge cases and risks. It may arrive "in core" someday, but it's going to be a very long road. I would suggest starting on one of your bullets. Pick as small of a feature as you can, then expand on its use case and all the specific items it would need to do. Look at Patroni (current best-in-class failover system for Postgres) and see how it does it, then try to map how Postgres itself could do the same.
