We aren't there yet but maybe in the next 15-30 years at the earliest assuming everything goes perfectly, which it never does. We still have a lot of work to do in regard to the neuroanatomy of stuttering and understanding how it works (speaking from someone doing research in this very topic). Also, research takes a looong time to go from testing to mass public use. There are a lot of steps to make something publicly available for treatment especially any kind of invasive neural stimulation.