> this doesn't get reasonably full access to the App Store then it's a no-go for me

From their page:

"Additional apps. HomeView supports compatible third-party audio and video apps from your iPhone for a familiar experience across devices"

This implies that Plexamp could be supported, and possibly Messenger and Snapchat calls, but it's too early to tell.

> My house has a bunch of spots on the wall where an old intercom system used to live: it'd obviously be a budget buster to buy a bunch of these to fit in those slots but even if you did, you'd need Apple to provide an intercom solution (a la the Watch's Walkie-Talkie?) or you're...out of luck.

Apple Home already provides this. It's not a full voice chat, but you can tap a thing and say something and it'll broadcast it to the rest of the house; in my case, that's two HomePods Mini, but it's easy to assume it will include this as well.

If you're just looking to say "Hey kids, dinner's ready" or "We have to leave in 15 minutes" to the entire house then that circumstance is handled already; if you want to have a back-and-forth conversation with someone in another room, though, it doesn't do that (yet?).

It sounds like it'll be integrating with the call and widget apis. Right now, you can redirect any voice call that uses the system call UI to your homepod. Adding video, maybe?