What's really going to happen is absolutely nothing. People won't throw away anything because people won't even know or care that Windows isn't being updated anymore.
The landfill isn't the solution because there isn't a problem.
I don't know if I totally agree with this. Maybe it's not nearly as bad as how the article frames it but just doing a Google image search of "landfills of old PCs" returns some pretty convincing images.
Hardware does become obsolete at some point and people will get rid of them but the EOL of an operating system is not the reason for it. As long as people can boot up and do whatever they want to do with acceptable speed then most won't upgrade.
Unless a big pop-up warns and nags users about it, I don't see Windows 10 PCs getting thrown out anytime soon.