I agree with the article, email is email. But it points out something which is fundamentally a problem for the industry. Some software is done as in doesn't need to change any more.
That is a scary place since all those Gmail engineers need to do something so if it isn't adding new things to Gmail what will they do?
Interesting parallel in open source, Linux especially, when you have a subsystem that works well and is well understood by lots of people. Nothing to fix right? Well that would be boring. So we get things like systemd replacing the init subsystem and we get the unholy love child of netware and windows 'net' command replacing networking infrastructure management. Did they need changing? No, the previous systems did just fine. But what else is there to do?