That said, task switching is a practical reality, so coping strategies are important, too.
For help with that, check out Cal Newport's "Deep Work: Rules for Focused Success in a Distracted World" (https://www.amazon.com/Deep-Work-Focused-Success-Distracted/...). Full disclosure: He and I share a literary agent.
While following the advice in the book did push my productivity up, sadly I didn't manage to keep up those habits. But it does appear to work, just need to make the right adjustments to make it easier to follow.
As the author points out, we've forgotten how to be bored. We need to learn to engage that part of our brain again.
He calls this "deep work" and has written about it in detail in his 2016 book of the same name: https://www.amazon.com/Deep-Work-Focused-Success-Distracted/dp/1455586692 . He emphasizes the increasing importance of such work in the knowledge economy.
Are there any companies or startups that allow their employees to work in this manner? Has this led to a different way of identifying tasks, structuring them and setting up the work environment?
It's sort of a bad thing to do, but you will start getting fewer Slack messages. People have an implicit understanding of who's likely to respond in a timely manner, and somewhat ironically, it's the most responsive people who have to improve their responsiveness even more because by being responsive they'll get even more messages and interruptions.
On a meta note, it continues to surprise me that more people and companies aren't talking about the highly distracting effects of the software. It works great at small scale, but if you get large enough everyone's pinging everyone all the time. I recently read Deep Work by Cal Newport (excellent book by the way ) and couldn't help but being mildly entertained when they get into the time draining effects of email (it seems to have been written a little before Slack caught on). The distraction engine created by Slack is the SR-71's Pratt & Whitney J58  compared to email's 5 HP motor out of an everyday golf cart.
The idea of people spending 10+ hours in VR per week scares me, but it's probably pretty similar to video game and smartphone usage. Maybe that would be a good place to start research.
A little over a month ago I started working on forming new habits, severely limiting use of network tools. I now only check email/sms/etc twice per day. At 6pm I put all technology away. I'm asleep by 9:30pm, awake at 5:30am, and try not to look at any network tools again until 10am. I'm considerably happier and more productive now. It's a tough habit to maintain and I'm pretty sure a few of my friends think I'm nuts.
A couple good, related reads: