But then, why would 10s of millions of people buy a Helix box if they can't play their games from Steam on it? That's where most of the PC gamers are on planet Earth.
Then that's kill anything MS wants to do with Helix then. At this point, it'll be better if MS paid Valve to have Steam on Helix.
Have you considered what the price will be for Helix? $1,200 - $1,500 means it can't reach 10 million units. And why do you think only 50% of Helix's sales will come from America? Currently the Xbox Series consoles are at 56% sold in America and 44% the rest of the world (25% Europe, 2% Japan, 17% everywhere else combined).
I'd assume Helix sales at least 60% in America, but maybe more when you consider how MS abandoned the Series console in Europe, the Middle East, and North Africa.