20-Year Prospect
The field of acupuncture is growing at a slower rate than most professions, but not by much (source). All sorts of things can affect demand—including numerous changes in the laws governing its practice in the U.S.—but remember, this field got its start in 6000 BCE so...yeah...probably not disappearing in twenty tiny years.
Sure, there are always shifts in cultural attitudes toward pseudoscience, but even in our most skeptical eras, we've never run them out of business. We wouldn't expect a boom any time soon, but we also wouldn't be too worried about getting started today on a lifetime career in acupuncture either.