Why? U1 chip really means nothing right now. Yeah it has some good possibilities but nothing I can think of that would stop anyone from buying the HomePod.
I'm not sure of it, but perhaps Ultra Wideband technology, which is what the U1 chip enables, could be used for wireless audio.
Airplay's sound quality is great, but as it's based on Wifi it inherently is power-hungry and comes with a lot of lag, making it difficult to implement system-wide for event-based sounds and require video content to be synced with lag. Bluetooth comes with data rate limitations.
Possibly UWB could enable high data rates with minimal lag and low power consumption, basically the Goldilocks of wireless audio. This would then possibly make it easy-peasy for Apple to enable things like system-wide stereo pairing with U1 enabled Macs for example.
This is just me speculating here, on the hypothetical basis that UWB can be used for wireless audio.