and even today, by using an old Android API iirc
Nope, the required API to have your app in the Playstore constantly rises, and if you don't comply you get kicked. The current API version is something around 26, and definitely has the permissions model integrated.
Can you still hibernate and suspend?
Well how do you want to use said get function?
let x = config.get("key").await;
So what type should x have?
You can see it in the image you linked.
+1, no problems at all so far, been using them almost daily for a year now on both linux and android.
What do you mean exactly? A running system shouldn't spontaneously break from not being updated. It's just that partial upgrades can break compatibility/dependencies, but running full system upgrades should be fine, as long as you pay attention to breaking changes and major version bumps. Also with timeshift it should always be possible to get back to a working state.