There are at least three ways that Apple could possibly, if not unlikely, surprise us with HomePod:

1. It messes with Siri — either by changing what Siri is or allowing for other intelligent assistants to be accessible through the device.
2. It opens up a HomePodKit or equivalent allowing third party developers to run apps on the HomePod.
3. It allows for push notifications to the device in a way that’s open to APIs and much more aggressive than Alexa or Google Assistant.

None of these are likely, but if Apple were to do any, it would tip a few eyebrows.