Same here. I love my Pixel Buds. However, they are setup on all my devices, I just have to go and pick to connect depending on which device I want to use it with. Not sure if there's a way around that, for any Bluetooth device.
I don't see why it couldn't just maintain connections to two devices simultaneously and mix the audio. I'm pretty sure there are Bluetooth headphones that do do that. Battery life is the only reason I can think of but they should still give the option.