It's a great article, well written, and I like the recommendations. Especially "Find a Mentor"! But I still think deliberate practice is overrated (in some fiels, especially programming): http://davidtanzer.net/deliberate_practice
Personally, I find side projects one of the least efficient ways to improve. I already spend 8+ hours a day "doing" at work. In contrast I spend less than 30 minutes a day at work learning and understanding theory, new concepts, and different approaches to a problem.
So I get a lot more value from focusing my "free time" on the latter.
"This is compared to us developers learning to touch-type or learning the keyboard shortcuts of our IDEs."
No. Deliberate practice for programmers is not limited to just touch-typing or keyboard shortcuts. It's actively learning to use new tools and environments, learning new languages, and learning different ways to program, such as functional or object-oriented programming. It's practicing coding in ways like coding katas.
It's digging into code that isn't yours and making the software do new things, and issuing a pull request upstream.
Deliberate practice isn't just "practicing." It isn't just mechanical. It's challenging, it's hard, and it improves you.
If you think deliberate practice is just practicing mechanics, you are ignorant on the subject.