The original HomePod will soon gain new features like 'Home Theater with Apple TV 4K' with support for 7.1 and Dolby Atmos as well as permanent Apple TV pairing.
HomePod as default TV speaker
Apple will add a handful of new features to the original HomePod through a software update to the HomePod itself and a tvOS update to Apple TV, both scheduled for later release.
First there is the option to set HomePod – or a HomePod pair – as the default Apple TV speaker, meaning that it will remain paired even after you set Apple TV to standby or after you stop listening to music on HomePod. This feature is already enabled in the latest beta software.

Photo: Reddit user samsam1029
- "Choose the default audio output where audio from this Apple TV will be played. You can temporarily connect to headphones and other speakers on tvOS," said Apple.
We expect it to work with both HomePod and HomePod mini – but not by mixing the two. You can connect a single or two HomePods to Apple TV. Once connected, the HomePod and Apple TV devices will be combined into one icon in the control center on iOS (as seen on the right). You will still be able to AirPlay to the HomePod, listen to music without turning on the TV, and use the speakers in multiroom.
HomePods can now be set as default audio output through Apple TV. (tvOS 14.2 & HomePodOS 14.2 both in beta) from r/HomePod
Home theater with Apple TV 4K
Apple is also adding 'Home theater with Apple TV 4K', which will work only with the original HomePod as it requires spatial audio support ('spatial awareness').
At this time, Apple's HomePod product page is acknowledging these capabilities in name only, without further explanation. However, the company has provided The Loop with additional information. Apparently 'Home theater with Apple TV 4K' will support Dolby Atmos in addition to 7.1 surround, 5.1 surround, and stereo.

Source: Apple.com
- "A new feature is coming only for the HomePod that will add an immersive home theater experience when paired with an Apple TV 4K. To get the 5.1, 7.1 surround, and Dolby Atmos, you need to pair one or two HomePod speakers to the Apple TV. This feature requires the spatial sound support of HomePod, so it isn’t available for the HomePod mini," said The Loop.
We do not yet know how it works and sounds, but we can imagine that Apple will use some of the same tricks applied to AirPods Pro to deliver spatial audio. With AirPods Pro, the effect is impressive.
Also read: Review: Apple HomePod (stereo pair with Apple TV)

On the other hand HomePod mini will have some features that are not coming to the original model. HomePod mini features WiFi Thread, which is a standardised mesh network under the WiFi system. It is also equipped with an ultra wideband chip that enables 'handoff' where you can more easily hand off music playback from an iPhone to HomePod mini (via a software update).
Some of the other new features announced for HomePod mini will also be coming to the original HomePod. One new feature, Intercom, allows you to send voice messages to other HomePods in the home.
- Source: Apple, The Loop, Reddit (2)