Or are you in an unintendedly unique position?
That doesn't seem to track with the article, or the articles/blogs linked from the article.
Lots of no-comments from the PTBs at Google... too bad. They could end the discussion one way or the other quickly.
I can't imagine my former TLM ever taking 20% time, but I can thoroughly imagine him encouraging every single one of his direct reports to do so, unless we were on a launch sprint.
I don't want to equate this with working at Google, because I don't have enough information, but here's my anecdote about good managers:
Twice before I've worked with spectacular managers. They treated their employees well, and acted as great shields against the political infighting inside the company. But both times, the managers were forced out, and the employees that depended on them to get interesting work done ended up quitting as well.
If this is indeed, as the TFA posits, a memo from the top being filtered out by a few good managers, in a short amount of time those managers won't matter; they will be forced, or burnt, out. Neither case is good for the company.
If you need humans instead of robots doing a job, that usually (increasingly, as automation advances) means it requires judgement such that pre-written inflexible rules will be inadequate to handle it sufficiently. Which means you need to rely on the judgement of people applying flexible rules for the best results.
Rather, I've always imagined that it's not that it'd be closer to the perks like "unlimited vacation time": you can't just decide "well I'm taking the next 5 years off", because that'd be a dereliction of duty. In other words, if you have the premier release of your main project coming up in 2 weeks, it may be in your best interest to not take that 20% time for the time-being, but instead use that time to fully ensure that your project has a successful launch. But, if you don't have any big deadlines coming up soon, and you're reasonably on schedule, then by all means take the 20% time.
The 20% time is a perk, and just like many other perks, your use of the perk cannot preclude any tacit duties that you may have, which include delivering on your assigned projects.
But, this is just an outsider's view, I could be completely wrong.