An inhibited adult, however talented in other directions, is virtually impossible to get improvising. Maybe that is the key to changing things - get children improvising as an integral part of their piano lessons.
I say old chap, have you been following "The Worlds Greatest Musical Prodigies" series, the last part of which is on as i type?I thought that young pianist was a good improvisor. Cannot remember if he was the one that got through.Thal