Ask HN: What sabbaticals are offered for SW and Research Engineers?

Most tech company sabbaticals seem to be of the blanket format "work here x years, take y months", where x >= 5 and y = [1, 2] (give or take, sourced from http://fortune.com/2016/03/07/best-companies-to-work-for-sabbaticals/).

Are there variations more tailored for engineers though? I imagine some flexibility in x and y if, for example, a SW eng. puts in remote work during their sabbatical. Or consider a research eng. taking time to pursue a tangential project that may pay dividends for the company when they return.

And the ~5 year minimum seems standard, but what about startups that have barely existed that long? Are there any options out there that may relax this rule, perhaps if the sabbatical is unpaid?