No Spotify support. Spotify’s market share is probably so large that Apple will sell fever of this speakers because of that.
The APIs required for Spotify to support HomePod are available, but as usual Spotify has yet to take advantage of them.
There is a long history of Apple changing the rules on Spotify [2]. Given Apple's focus on promoting their streaming services, I would not be surprised if Apple is intentionally trying to pressure Spotify into a narrow lane as far as integration options. They wouldn't want to cannibalize their own streaming ecosystem.