Isn't the 20% time to work on whatever cool shit you want enough ? (like how googlers created that garbage angular1 because they were border, have no clue about GUIs and had some fun scewing around ) ? I know people that are fine with getting paid to maintain shit so maybe the problem is Google only hires cool developers and the cool developers only want to work on cool stuff and in 2 years the newest cool stuff of-course.