Will this affect current visa holders, new applicants, or both?

Both. Applicants who are holding valid 10-year B1/B2, B1 or B2 visas issued before November 29, 2016 will have to enroll in EVUS to use their visas any time after the launch of the program. Applicants who receive 10-year B1/B2, B1 or B2 visas from November 29, 2016 onwards will have to enroll before their initial trip to the United States. Enrollment for all applicants will remain valid for two years or until the traveler’s visa or passport expire, whichever comes first. The visa holders will then have to update their information before traveling to the U.S. again.