It'd be nice if folks were actually discussing the topic (release of HomePod firmware via the IPSW server). Doesn't anyone get tired of every front page story being turned into the same, tired Tim Cook vs. Steve Jobs/Apple Isn't Innovating Anymore debate? (Please, someone, say something about HomePod being overpriced, or that it has insufficient RAM! /s.)
My takeaway from the actual story is relatively boring. I have to leave it to people wiser about code to tell me what that firmware can do. So far, they've only given us a few tidbits. Undoubtedly, coders will take a deeper dive into the system in the coming days and weeks.
1) Why would Apple put this out onto a publicly available server, other than to test the OTA update process? AFAIK, there are no review units in the hands of journalists or developers, so that's not yet a reason to push revised firmware out beyond the R&D firewalls.
2) With Apple knowing that this would leak, I'd expect the first release to be bare bones - no bundled apps, just an answer to the question: "Will a firmware/OS upgrade install correctly?" Whatever is released with the product in December, it's going to have more than we see here. It's too soon to pronounce the OS either stupid or brilliant.
3) 32 x 32 is a standard-sized icon, part of a standard app distribution. I can imagine the icons being desirable for displaying system state during initial pairing/connection, and if there's to be a third-party app capability, for displaying the running media app (Apple Music, Spotify, etc.). Unless the button is huge, 32x32 is plenty - why over-build and raise the BoM costs unnecessarily? This is a unique display for Apple, so it requires new code. There's an existing code base for a wide variety of touchscreen displays, so if/when we see a touchscreen-equipped HomePod, that code will find its way into the distribution.
3a) I won't bet any real money on it, but I find it hard to imagine they don't intend to support third-party music subscription services - Apple makes very good money selling subscriptions to competing services on iOS and tvOS. If someone purchased a Spotify subscription through the App Store for their iPhone, I'd imagine they'd be very unhappy to learn they couldn't use it on HomePod - fewer HomePod sales is not a good thing. Sure, Apple said, "Apple Music" in the Keynote. They're not going to promise a capability or name names until they know they have other services on board.
3b) It'd be very like Apple to release an Apple Music-only version in December, with a promise of third-party app availability with the release of PodOS 1.1 or 2.0.
4) For HomePod, third-party apps will be dependent on the capabilities of SiriKit. AFAIK, SiriKit does not (yet) have an Intents Domain (vocabulary) for music/media. It has to exist, but for now it's apparently still Apple-internal. Again, presuming there's support for third-party music services over the horizon, it'll be rolled out when they announce third-party support.
5) To see where HomePod is likely going media-player-wise, take a look at tvOS. I'd expect Universal Search at some point in the near term - Apple would rather sell two or three music subscriptions per user, rather than just one.