Benjamin Mayo, 9to5Mac:

Whilst HomePod works best with an Apple Music subscription, allowing users to ask Siri to play any of the 40 million tracks in the Apple Music catalog, it does not require a subscription to function. We have learned that the HomePod can play content purchased from iTunes, stream Beats 1, and listen to podcasts without needing a subscription.

And:

Users can continue to buy albums from iTunes and expand their collection of purchased songs associated with their iTunes Store account, and ask Siri to play those on HomePod.

But:

If you add music to your home iTunes library that was not acquired through a purchase, HomePod will not be able to access it. It appears HomePod doesn’t have Home Sharing, which would enable that kind of feature.

Judging from the huge HomePod interest on my Twitter feed, and from the volume of questions I’ve been getting on issues related to HomePod and Apple Music, I think HomePod has big potential.

In the short term, buyers might skew heavily towards folks already subscribed to Apple Music. But I see HomePod as a potential Trojan horse, bringing new subscribers to Apple Music, assuming the HomePod reviews are positive.