Yeah, I wish audiobooks would become more cloud-integrated. I’ve been wanting an Apple TV audiobooks app for ages, as well as real syncing and storage via iCloud. As it is now, you can redownload your purchased audiobooks all you want, but the ones you see in your app are physically on your device - they’re not really a part of iCloud for iBooks. Hopefully the next version of iBooks/Books will fix this, because once audiobooks are fully integrated in the cloud, it should be very easy for HomePod and Apple TV integration to happen.