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»And the world is like an apple whirling silently in space, Like the circles that you find in the windmills of your mind.« (›Windmills Of Your Mind‹ [1967]. Music by Michel Legrand ; English lyrics written by Alan & Marilyn Bergman)
Sonos doesn't even support regular DTS, much less DTS-X. The bandwidth available via optical (384 Kbps) isn't enough to handle 7.1, Dolby Atmos, DTS-X, or any of the newer theater audio formats. It can't even handle uncompressed 5.1 audio. And even if the Playbar and Playbase supported HDMI-ARC, there's not much more bandwidth available there too (~1 Mbps, still not enough to support uncompressed 5.1 audio).
HDMI 2.1's Enhanced ARC (eARC) promises to be a significant upgrade over the regular ARC available now. It's not expected that any 2018 model TVs will have it though. I'd expect to start seeing HDMI 2.1 in TVs starting next year. According to the HDMI forum, some features - including eARC - could be implemented via firmware upgrade to HDMI 2.0 devices... but that's up to each individual device manufacturer to support. Another big feature of eARC... there is a mandatory requirement for data to automatically correct lip sync issues!
Whether Sonos will have something new to support HDMI 2.1's eARC is, of course, unknown.
See the attached table below for more comparison of Optical, HDMI-ARC, and HDMI 2.1's eARC. This table came from a FlatPanelsHD article on HDMI 2.1.