Indeed. You are not an expert in this field. I am a practicing nuclear medicine physician who had multiple jobs offers at time of graduation. Even now I get offers from recruiters and colleagues who are looking to hire additional staff. At my current place of emplyoment, we have more work than we really want!PET/CT is the fastest growing imaging modality at the moment. Your point re: PET/MRI is taken. However, since 2007 NM has expanded to a 4 year residency (internship + 3), and cross sectional imaging including MRI is part of the curriculum.
Like you said, no one has a crystal ball. I can only share my experiences and those of people who trained with me, just before me, and right after me. The total number of individuals is approximately 25. Of these, only one (yes one) had difficulty finding a job, and thats because they were unable to pass the boards. Unlike IM, FM and other fields, being board certified is integral to getting "a" job in NM, and to a lesser extent radiology. It used to be a cakewalk to get into NM residency. And indeed, many FMGs would go into NM because they could not get anything else. It is changing, albeit slowly. At the time of my graduation, all applicants at my ex program were US grads, and two were MD-PhD.
To Nukedoc: feel free to ask any questions that you may have about this field.