You are not very specific. Therefore, it is hard to answer your question. I did my PhD on EALs (children learning English as an additional language). In other words, children with special educational needs. When I wrote my research proposal I was truly interested in the subject and I didn't think much about my career options. Now I am 4 months after my viva and I haven't found the job related to EALs (despite the fact that there are 1,000 000 children in the UK). Fortunately, my study was purely quantitative (randomised controlled trial) and I hope that my skills can be used in other sectors. Besides, I applied through my university for a grant related to EALs. My advice: Go for it if you are really interested in the topic. Be flexible. Focus ion developing transferable skills. Create job opportunities. Be positive and don't think too much about 'the career opportunities it might bring'.