Regarding the mono/stereo debate:
this article from The Verge has more information about the type of processing that's going on what what the HomePod outputs. The gist of it is that the HomePod does a different form of sound-staging and separation than traditional stereo. The whole point of stereo is to create the illusion of discrete sounds in space. The traditional method of creating those discrete sounds in space has been multiple speakers physically separated from each other.
With modern beam-forming technology, it's possible to create discrete sounds in space from multiple speakers in one enclosure. Apple could have chosen to apply the beam-forming technology and multiple speakers to duplicate the effects of two physically separated speakers. Instead, though, they're using signal analysis and processing to pick out what they call different "aspects" of music and are using beam-forming to place those different salient aspects (such as a piano, a vocal, or a guitar) in space. So it (theoretically, we'll have to wait and see how it does in practice) achieves the same goals as stereo sound, but it doesn't use the same recreation methods as stereo sound.
But Apple does provide the option of pairing two HomePods, applying their analysis to left and right tracks separately.
So is a single HomePod mono? In effect, not really. The multiple speakers in the HomePod doesn't serve the purpose of multiple drivers in a traditional loudspeaker, which are for splitting up the frequencies across the drivers. Rather each seems to be a fully discrete unit. So it's not going to produce the same type of uni-directional sound as a single traditional loudspeaker. But a single HomePod isn't stereo in the traditional sense either, as it's not using the separate left and right tracks to produce its sound staging effects.
The main takeaway, for me anyway, is that most audiophile purists are probably going to hate this. Their goal tends to be a faithful reproduction of what the artist and sound engineers intended. That means precise placement of instruments with as little processing as possible from source to ear. I get that, and I respect it. But setting up and maintaining such a system is an investment of both time and money (I know from experience). My priorities are different now, and my desires lean more towards unobtrusive technology that can still produce nice results. I don't have a whole lot of time to sit in a sweet spot and just listen to music, but I do want some good sound while I'm doing things around the house. I have high hopes for the HomePod because of this, but I fully understand why it's not everyone's cup of tea.
