I would think that most areas of medicine, except surgery, surgical subspecialties and some medicine specialties would allow either part-time work or a shared position.
To work part-time and still be >100k - EM, Anesthesia, Rads, Path, Derm
My thought is that you can essentially work in any specialty part-time as long as you are willing to take the pay cut. There are many large groups and hospital employers that like taking on a few part time docs in all specialties to make things easier for their full time docs at a fraction of the cost. Even in primary care, I have a cousin who works as a pediatrician once per week. Other physicians in her group/hospital cover her calls for the rest of the week.