For this specific plan, it asks a 35-year-old to agree to work an additional year in their 60s for 3 months' sabbatical in their 30s. That's a pretty bad deal, not only because of the imbalance between what you gain and what you sacrifice, but also because there are so many unknowns about your ability to work in your 60s. And how do you really enforce something like that?
But in general, one major problem with sabbaticals is that they are almost always tied to your employer and require you to rack up multiple years of experience to qualify for them. But the trend over the past several generations is toward greater job mobility. It is relatively rare for Gen X and Gen Y workers to have stayed with one employer for decades, as many of their parents may have done. Job hopping is often the best way to increase one's compensation, and the loyalty that used to be shown between employers/employees has largely dissipated.
Thus, many people's only realistic chance at a sabbatical is to do an unofficial one by taking some time off between jobs -- but this has its own problems. Since health insurance and many other benefits in the US are tied to employment, it can be extremely costly to not be constantly employed.