The switch came out 4 years after the wii u so it's possible for a portable xbox one x to come out 4 years after the xbox one x
I'm not saying it's impossible, but that is not how technology always works. It could maybe happen, but it's not a linear year requirement for every system.
In my opinion Microsoft should consider to leave the console market. Since they entered this market I asume they lost more money than they gained.
I think Microsoft should consider becoming a challenger to Steam by making bold steps into the Subscription-based games service. Whether or not it will be seen as favorable, I don't know, but it would certainly be interesting. However, I think it's fairly likely that they'll still make a fourth Xbox.