It's up to Netflix. Nothing Roku can do about it. Yes, Netflix is really taking their time with their rollout. One more reason I cancelled my Netflix account.
Want to agree with the comment by CSmyre64 about Atmos support. I watched Hobbs and Shaw on Vudu in 4k with full dolby Atmos sound over my Roku Ultra and Denon AVR X6300H on 10/20/2019. On Netflix 4k streaming using the Roku Ultra 4670RW I get a selection for Dolby Atmos/ surround sound in a pop-up box on my TV screen but then the AVR displays Dolby Digital+ +DDS when the pop-up disappears. The Roku literature (and my Denon) states that Atmos is available as a pass through on their units and it sounds great. I've had the same results on HBO and Showtime.