Think of it like, if your read-only regions don't have anything else stateful they're able to do before the postgres write fails, then their existence is indistinguishable from network latency. An app that doesn't break because of latency won't break because of this.

If the readonlies might do something else stateful and not unwind it on postgres write error, then this approach won't work. (But wouldn't they be buggy anyway? Postgres writes aren't guaranteed not to raise errors.)