I always think back to the Apple-Samsung patent trials which included images of early iPhone prototypes as submitted evidence. There are some truly wacky designs in there. Nobody would believe that an angular phone would have been even been considered by the likes of Jony Ive and Steve Jobs without these court disclosures.
Apple surely experimented with a much larger smart speaker chassis, probably to identify the best balance of audio quality and physical elegance (size). I would be shocked if the HomePod line gets larger before it gets smaller. The average person will already struggle to differentiate the superior sound signature of the HomePod compared to rival products. Going larger would merely target a segment even more niche than the market it already appeals to.