They are paving Navajo 20 which will shorten the detour by about 50 miles. That should be ready in the fall, and will be labeled 89T.
They also announced plans for fixing the slide on US89, but that will take a couple of years.
US89A was the original route. It crosses the first bridge over the Colorado between Las Vegas and central Utah, Navajo Bridge. Well, technically, it now crosses a parallel span. The original is open for walking. The Page crossing dates from when Glen Canyon Dam was built.