Our CEO has a domain of "Employee-related policies, including compensation and the company handbook". In v1.0 of the handbook he created, our vacation policy is basically "we're all adults; check with your team, and make sure you get your work done".
At our last company-wide meeting (not a holacratic one), he said he's worried as we grow this policy will break down. (In case it's relevant, there's no indication our team size is increasing anytime soon.) So he shared his current idea: release dates on a quarterly basis for two quarters ahead of time, and then those with the most seniority (time at company) get first dibs. He then invited input / feedback that felt uncomfortably consensus-based to me.
My modest experience to date suggests holacracy excels with role-based concerns, and doesn't translate as directly to "soul"-based concerns. Just as there are "apps" for compensation, I'm wondering if the same is true for vacation policies.