Please consider prioritizing this. I'm tired of not being able to conveniently voice command Spotify in iOS and I don't think I'm alone. I know this has been Apple's shortcoming for a while, but it now seems possible and I'd personally like to use Siri from the watch to play a song or start a playlist. I know the in-app voice command was added and I've used it once or twice but it's not convenient at all.
iOS12 was released to developers months ago. It entered beta months ago. Spotify should have this ready TODAY, upon iOS12 release. We've been waiting for this for an eternity, get your stuff together guys.
Loxer was correct that iOS 12 wasn't out at the time of the initial reply (a day before the official public release), but as others have pointed out here, it's been available for developers since June.
A large number of apps had this integration ready to go on day one (Pandora for instance). It feels like Spotify really dropped the ball on this one.
No longer up to Apple. As mentioned above, iOS 12 beta has been available to developers for a while now and the public version has now been released. It is up to Spotify to decide whether they want to develop a feature that many of their users have been longing for for YEARS. I will wait a couple more months for an update, and if this continues to be a non-priority, I'll be taking my paid subscription elsewhere.