I took the fast.ai course and now I am doing a Ph.D. in Biomedical Engineering focused on applying deep learning to microscopy.
I don't think fast.ai is enough if you want to do theoretical research in deep learning, but it certainly provides enough to work on practical problems with deep learning. That said, many of us in the fastai community are able to delve deep into, understand, and implement recent deep learning papers and even develop novel techniques. So I think with a little extra studying, one could go easily transition to core deep learning research.
I don't think fast.ai is enough if you want to do theoretical research in deep learning, but it certainly provides enough to work on practical problems with deep learning. That said, many of us in the fastai community are able to delve deep into, understand, and implement recent deep learning papers and even develop novel techniques. So I think with a little extra studying, one could go easily transition to core deep learning research.