I don't get why pulmonary fellowships aren't more popular. Here we have one with one of the best pathologists in the world and not much interest. I considered doing it for awhile, in place of general surg path, because there is so much overlap, then apply for GU. But they gave me GU so I didn't do it. The thing about pulmonary is that every medical pulmonary biopsy is difficult unless:
1) All they biopsy is cartilage or blood clot, in which case it's easy
2) There are some granulomas, at which point you can stain it and sign it out
3) It's obvious cancer.
Everything else is tough (which is over half of the transbronchs and all of the medical lung open bxs). But it isn't marketable because the volume is not so high out of the large academic centers, and even then it isn't that high. But even pulmonary pathologists say that it isn't a marketable subspecialty, although they also say that none of them have trouble finding a job because they are usually excellent pathologists. As I have said before, this is a factor that is often overlooked by young trainees when it comes to job related issues: Being a good pathologist is important. Even more important than fellowships!
I went and looked at job postings out of curiosity, it seems like the majority of the ones looking for "GI" are looking for someone with "GI interest or expertise" and less than half of them ask for a "GI fellowship." Personally, I plan to spend a lot of my fourth year and fellowship year learning about GI also, but not doing a fellowship in it.