I am not currently a medical genetics resident but a trainee in genetic counselling, and working in medical genetics for over a year now, I've developed substantial knowledge of the field. The role of the medical geneticist seems to ironically be threatened as the price of genetic testing gets cheaper. As the price of sequencing falls, it is more economically effective to conduct high-throughput diagnostic methods such as exome sequencing, and less necessary conduct a dysmorphology exam to propose a differential diagnosis and narrow down a genetic test. Therefore, the medical geneticist, with their specialized dysmorphology training, is seen as less relevant. What's more, as genetics becomes a more integral part of medical care, genetic testing companies have figured out ways to market their tests in a simpler way for physicians without genetics training, offering next-generation sequencing panels for all of the genes that can predispose to a particular observed symptom/disorder.
However, all this being said, I don't think genetics is a diminishing role but rather an evolving one. In the past few years it has become common clinical practice for neurologists/pediatricians/neonatologists, etc. to order diagnostic microarrays. They are perfectly capable of ordering these tests, but once the results come back, they do not have the knowledge or experience to interpret them. Often these tests come back with variants of uncertain experience, which are challenging for both patient and physician to handle. These cases inevitably all end up getting referred to us. It is possible that as time goes on, medical genetics will become less of a pre-test diagnostic, and more of a post-test interpretative specialty.
The nature of genetics is that it is constantly rapidly changing, and with rapid change inevitably comes a bit of uncertainty. Further, because genetics is preventive medicine, it is a specialty that hospitals will cut before something more immediate such as emergency medicine. Therefore, I would not recommend entering genetics if you are simply looking for a secure profession, due to the growth of the area. However, if you are genuinely interested in genetics, it is a fascinating area to practice, and I wouldn't worry about it "dissolving" anytime in the near future.