As background for my work on discussion arcs, I've analyzed the distribution of research interests among research-oriented philosophers. Maybe some readers will find the data interesting.
My sample of research philosophers is non-emeritus professors with their primary appointments in Leiter top-20 ranked Anglophone philosophy departments -- 548 professors total, by my count. I noted the areas of research interest these professors listed on their departmental websites. Most philosophers listed about three to seven areas.
First, I looked at area of specialization, counting only the first listed area:
Then I looked at all listed areas of interest:
I also broke down historical interest by time period (splitting out Asian as a separate category):
Two things jump out at me from these data: first, the almost complete lack of interest in Asian philosophy among Leiter top-20 faculty; and second, the much greater rate of interest in metaphysics and epistemology than specialization in them. Here is a chart displaying the ratio of interest to specialization in the various subfields.
Almost five times as many philosophers list epistemology among their areas of research interest as list it as their first area of specialization. Philosophy of action shows an even higher ratio, though the total numbers are smaller. In contrast, philosophers tend not to express research interest in ethics or philosophy of science unless they list them as their first specialization.
On Continental Philosophy:
I also looked at interest in "continental" philosophy -- that is, interest in 19th and 20th century figures in the German-French tradition, like Hegel, Nietzsche, Heidegger, Foucault, and Derrida. Although top-ranked Anglophone departments have a reputation for hostility to 19th and 20th century continental philosophy, 45 philosophers (8.2%) listed continental philosophy or a continental figure among their research interests, an average of 2.3 philosophers per department. About 20% of Anglo-American research philosophers who express a research interest in any area of history of philosophy express a research interest in continental philosophy.