Now why do you think there have been no answers? Maybe the question was a little unspecific???
I'm just going to throw in some ideas for you. I'm a clinical physio with a number of CPD courses in neuro anatomy and physiology and Bobath principles and light years away from being a junior physio and studying.
"Neurorehabilitation" is an enormous field. You may not have had much clinical experience yet but you must narrow this field down a bit I think. We have (small selection): Childrens and Adults Neurorehab; Cerebral palsy ; Stroke; Traumatic Brain damage after accidents; MS; Parkinson; Acute in hospital; Chronic at home or outpatient level......endless lists. All treatments based I hope on a good assessment and good knowledge of Neurohysiology combined with the practical application of it.
You have to maybe do something that has really interested you at undergraduate level or in clinical experience. The "passion" to persue something should really come from your ideas......which you must have or you wouldn't be doing an MSc in Neurorehab. May be a silly question but why "unique and controversial"? Does your MSc have to be really clinicaly relevant or what????
One field could be the use of robots and complicated machines to "replace" or "enhance" real physios. Or "neuroplasticity for ever" versus "the stroke was 3 years ago it's no way going to improve now"
Now "thinking cap" "on" and discuss ideas with a tutor pehaps.....there are probably a number of Neuro physios out here who could help if the question was not like "how long is a piece of string".....neurorehab is fascinating go for it with passion!