But I already said that the consoles will be sold to hardcore Xbox fans..... we both agree on that. The issue is that most people won't even know that they exist with a 10 million niche consumer base. Look at the Wii U and PSVita, for example.
The best case scenario is that MS sells their future consoles online no matter how much their console business declines.
The PC initiative has been going on since 2016, yet the console has continued to sell. That's because for the most part the people who buy a console buy one to play console games. Outside this forum there isn't that much overlap for high end PC gaming and console gaming.
The XB1 is a platform as you have mentioned has had many turnarounds this gen. The system with all it's mess ups, lack of exclusives and exclusives announced to appear on PC since 2016 has managed to sell 40+ million. PC has devalued the box for someone who has a higher end PC capable of running the games. That happened a while ago and for the most part the system still sells. The system is a failure compared to the 360 but 40+ million for a console is still solid.
The streaming argument killing consoles has yet to even take place in the market. It's the same thing as the mobile audience killing consoles, there isn't data on it. With the U.S having terrible internet infrastructure to support widespread streaming, it would take longer to even determine it's effect of killing console sales. Xbox console sales aren't about to drop from 40+ million to 10 million outside a colossal mess up next gen. You can argue a decline but you can't argue a decline to 10 million units outside some crazy mess ups.
A system that is considered the worst Xbox for exclusives will likely have a successor with a higher quantity of console exclusives released.