The AAN has joined several medical societies aiming to push for Medicare to set reimbursement rates (i.e.: level V consult, procedures, etc.) based on board certification and/or re-certification status. If this get enacted at a point within 10 years, it will result in changes in how many people get subspecialty certification. Think about the possibility that your EMG might be paid only if you are currently certified on Clinical Neurophysiology or Neuromuscular (or similar boards for the PM&R). This is not far-fetched as it seems, but for current residents it make change fellowship decisions.
At the present time, Clinical Neurophysiology is the most popular fellowship (over 200 slots/yr) because it allows you flexibility for private practice (BC doing EEGs, EMGs, and for the last year Sleep studies). Out of my last 10 fellows, half of them decided to use their CN fellowship to cover their requirement in Sleep Medicine (and get BC in Sleep). All of them are in private practice. That loophole is closing.