This is just a rumor, but it would make sense. Roku introduced its voice-controlled home theater software, Roku Entertainment System, earlier this year. Along with Roku Connect, it's a way for users to operate their home theater systems wirelessly through voice control. Roku isn't building its own speakers, though; their new endeavor is purely software that they'll license to third parties, hence why it makes sense that they might be working with Sonos.
If the rumors are true, this partnership would allow for voice control of both your Roku and your home theater system via Roku Connect. Because Sonos One is the only Sonos offering that currently supports voice control, functionality would likely be limited to this speaker.
It's possible that this could all come to nothing, or not even be in the works. But it makes sense, given both companies' stances and recent product announcements. Sonos has integrated Alexa into its speakers and has a stated goal of supporting Google Assistant by year's end. Supporting Roku goes right along with their current strategy.