He's the least technical "technology columnist" I've ever read.
Being a supposed technology columnist, he should have been aware that yes, text is still often rendered in monospace fonts. His grasp of history is just horribly wrong: "Monospaced fonts went out in the 1970s. First electric typewriters and then computers began to offer people ways to create text using proportional fonts." He's talking about exotic hardware that was used by approximately no one.
Being a supposed technology columnist, he should also have done some research to find out how single and double spaces are rendered by word processors and email clients. Double-spacing is perfectly fine if word processors know what two spaces after a period mean and render it appropriately. I was taught that they do, so for me, double-spacing after a period seems like the perfect solution: double-spacing is the least bad solution for monospace fonts, and for proportional fonts, a double-space after a period will automatically be rendered correctly. If he wanted to do an actual service for his readers, he could have told us whether that is true or not. Since he is, you know, a technology columnist. Doesn't that title imply something beyond the ability to review smart phones?