I have the Chromecast ultra and after realising that it didn't support Atmos, after having built an Atmos system I did some further research.
It's a bit of a minefield and is not only dependent on the streaming hardware, but also the streaming service itself.
From reading, the conclusion was that Apple TV 4K is the best option if you want Atmos, and after buying one, I can confirm that I now get Atmos on Disney+, Netflix and Prime (I also have NowTV who charge you extra for 5.1 but don't support any content in Atmos!)
In answer to your question, I think it's too early to know with the new Chromecast, but that didn't stop me preordering one. I'm hoping that before it arrives, someone on the internet will confirm either way and I'll either cancel the order or keep it.