I see by Googling that HA has at least some (beta) tie-in with Android Auto, but I can’t seem to find out the current status. There’s no “Android Auto” integration. Using the Search function on this forum mainly reveals that “Android” and “auto” are unfortunately very commonly used words 
Is there a subforum, Reddit, Github project or some other place where I can see what’s going on?
The Android companion App seems to be where all the work is going on.
Android auto support is offered through the Companion app. You don’t need an integration.
It can pull some sensors from the car (if your car allows - most don’t) and offer notifications in dash and a quick access panel for up to six entities. The entities for the in dash shortcuts must be simple on/off entities for now as Android Auto has limited support from what devs can put in the interface - so cameras, or anything that requires complex controls (keypad for an alarm for instance) aren’t currently supported.
Is that in the current app or just a specific beta version?
Where do I find the details on this?
It’s in the current app (I think it’s been there for nearly a year or so now?).
Wow, i didn’t know that, do you have more information on this? I just have one sensor indicating if my phone is connected to android auto or not.
Found it here: Sensors | Home Assistant Companion Docs
It shows up in Android Auto. On the dash display, after a very long spinning cursor, it puts up a single icon labelled “Navigation” which does nothing.
And that’s it. How do I populate that screen with something useful?
Ok I found this:
I’m assuming that in order to use this, you have to be subscribed to HA Cloud access, right?
Nope, it’s just part of the companion app when you plug your phone into your car, like any other android auto capable app.
So, when you’re a mile away from home, how does Android Auto access your HA instance at home?
Same way you access HA with your phone when away from home. So yes, that could be Nabu Casa or any of the alternatives.
There are multiple ways tk setup access outside of home and NabutCasa is indeed one of the but you could also set up your own SSL tunnel, tails ale, cloud flare, or SSL access from outside with a reverse proxy and DuckDNS.
Android Auto through the companion app just uses what you setup.