How is AM stereo doing in the US?

Just about dead. Few receivers available except for some OEM car
radios, fewer and fewer stations broadcasting it.

But there are still more than 10 times as many AM Stereo stations as
there are AM stations using IBOC. And as for "fewer and fewer
stations broadcasting it", you could say that about IBOC -- within my
listening range here in NJ, there are at least half a dozen stations
which tested IBOC for a few weeks or months and then gave up on it.

For example, iBiquity's web site lists 860 WWDB in Philly and 930 WPAT
and 1480 WZRC in the NYC area as current IBOC signals, but all of
these stations haven't transmitted IBOC in almost a year now. This
kind of track record does not inspire much confidence in the future of
IBOC, at least on the AM band.