When I was a kid, my father got a sabbatical - he was a professor in a respected design program in a relatively well known area of the US. I struggled to comprehend how it is possible and this sounded like an incredible luxury; offered only to tenured, old respected faculty. Without the constraints and demands of his normal 10-2 academia job he wound down into a productivity-free state in which he did very little aside from his usual scribbling and sketching of ideas on scraps of paper and generating loads of notes. Not that many years later he retired.
While it didn’t seem to me like the lack of results for the sabbatical were the main problem, knowing him full well I have this hunch that the sabbatical was really just a politically gracious way to get rid of him for a year, so that it would be even easier to get rid of him later for others who wanted his position, influence, whatever within that university.
If my employer offered me a sabbatical I would be suspicious.
I think given a sabbatical I would do exactly what I already am doing, which is an attempt at building a small community around our product (with an SPA/webapp) while using that as an opportunity for UX testing and research with users of our products which are surgical simulation devices.
I am not a fan of the sabbatical because that is too long to go off working on something without bringing it back for feedback/scrutiny. But I do think companies should give employees at least a day or two a week of freedom to do the projects that interest them for personal growth within the scope of the company.