ah, an important note: standby machines are only started when the host goes down, not whenever the primary machine is stopped.
I agree! there is a decent amount of technical work behind such a feature though, so it is unlikely to happen anytime soon, unfortunately.
(there is also some UX work to do: it is not possible to use the same egress IP across regions, so would need to decide on UX for scaling up to new regions, etc…)