So Alexa and Cortana are now starting to integrate
It's very early in the integration, but you can now 'Open Cortana' from a Echo device. I tried it on my Show and it works fairly well. It's an odd experience though, as it's like my echo now has a split personality. And I honestly can't quite grasp where this is a benefit to me, but it's got me wanting to explore what features Cortana has. And of course, this is not available (yet?) on the Sonos One or Beam, as it's not available on any 3rd party alexa devices. Without knowing the tech or licensing required in these, hard to know that it can be easily done.
The other side of this is that you can now 'Open Alexa' from a Cortana device, or at least a windows 10 PC. Eventually, it should be available on windows phones, a Cortana app, or xbox as well. I didn't think to test this last night, but in theory you should be able control Sonos by means of Cortana now. Just tell Cortana to open Alexa, and then give a voice command as normal. I can see this being rather useful for a home office, where you can control through the TV, or through an xbox (although you need a Kinnect or headset to talk to Alexa).
Maybe more interestingly, in theory, Sonos will be controllable through 4 different voice assistants by the end of the year,
"Siri, play XXXX on family room"
"Alexa, pause the music on family room"
"Cortana, open Alexa, resume music on family room"
"Hey Google, turn up the volume on family room"