So about 2/3 what the 360 sold lifetime. I have a feeling the Xbox Series X will be a much bigger success for Microsoft.
I do too, 360 era ended with MS shifting away from core gamers to casuals with Kinect then followed that up with the huge PR blunder to start XBO with no used games, always online, Kinect required, 2nd tier countries, $100 more expensive than PS4, etc.
They are ending XBO more similar to how Sony ended PS3 by releasing a great new service (PS+/Game Pass) and investing more into high quality first party studios.
As long as they dont make any unnecessary mistakes to start XSX like they did with XBO than they should be able to build off of that and have more success.
I think this will cause PS5 sales to not reach PS4 but still have a comfortable lead. I'll go with
XSX-65 million (up from ~50m XBO)
PS5-110 million (down from ~125m PS4)
Obviously this could change as we find out more about these devices but that's my initial prediction.
When the herd loses its way, the shepard must kill the bull that leads them astray.