The author has really limited understanding of the enterprise world I believe.
Email doesn't belong to a company? Nice one. It belongs to Google and Microsoft.
And this kind of change signifies three things immediately:
1. Being terrible means it's likely to happen and not really stoppable. They've already thought about how many people won't like it and still decided to go for it.
2. They try for a long time to have this more interactive messaging experience. Thinking Google Wave and Google Plus here. They have not understood that Slack/Wechat have solved that in a much more elegant way already. So they try again and again. This one will also fail to produce the vision they have. Google simply doesn't get that Web 3.0 interactivity. For us it's okay, it just means at some points other companies will take Google's place, and it will become that old, annoying giant like IBM and Microsoft before them.
3. Touching Email in this way also means that they are becoming desparate. Maybe not about profit yet, but certainly about the visionary aspects of the company. Email is one of their core components. You don't F* with those unless you really feel desperate.
It is not at all about users. It's about survival. Therefore the arguments presented in the article aren't even close to being good. A good article would figure out why they are so desparate and suggest things that they could do in favor of their users that still will increase their survivability.
Buying Slack and integrating it with their office suite might just solve their problem. It will be super expensive but might bring them onto the next level. Just a quick, stupid suggestion as example for what the article should've been about.