Considering how bad Xbox did the last 2 years, 9M at the end of its life seems like a lot for me.
Not impossible. What this really means is Xbox needs more than just BC and Game Pass to really make a point next time around. They need compelling, exclusive, software to generate early hype while maintaining an affordable price, key marketing, and a system that doesn't get trounced in the spec department (though this is highly unlikely anyway).
With the right combination, hitting 60-80m next gen would probably be achievable.