Australian Bureau of Statistics
4177.0 - Participation in Sport and Physical Activities, Australia, 1995-96
Basketball - estimate was 240,200 participants aged 15 and over, nationally. Participation rate of 4.6% of the population aged 15+. Given the overall participation rate for all sports was 30.7%, that meant about 1 in 7 people playing organised sport were playing basketball, for 15+ population.
Latest edition of the same publication is 4177.0 - Participation in Sport and Physical Recreation, Australia, 2013-14
Basketball - estimate was 406,100 participants aged 15 and over, nationally. Participation rate was 2.2% of teh population aged 15+. Given the overall participation rate for all sports was 60.2%, that meant about 1 in 25 people playing organised sport were playing basketball, for 15+ population.
So numbers have gone up but basically in line with population growth, while broader participation in sport has increased more rapidly. That increased general participation is across all age groups but most marked in 45+ age groups, where participation has risen 2.5 times what it was in 1995-96.
The 1995-96 survey may be a bit late for the start of the Jordan effect referred to by the OP, however another ABS publication (1301.0 - Year Book Australia, 1992) states:
"A Sports Participation Survey was conducted by the Australian Bureau of Statistics throughout Victoria in October, 1989. ...
The survey collected a range of information from persons in Victoria aged 15 years and over and covered the twelve month period ending October, 1989.
During this twelve month period a total of
1.378 million persons (41.7%) participated in
sport.
...main sports participated in were ... basketball (4.2%)..."
So this participation rate for basketball was consistent with the 1995-96 national survey, with about 1 in 10 people who played sport choosing to play basketball, for 15+.
So basketball's popularity among those choosing to play sport has declined over the last 20 years, based on these numbers, among people aged 15+. Basketball participation among kids aged less than 15 I believe has always been pretty high but I haven't tried to find any stats on what has happened over the last 20 years for that age group.
FWIW, I was involved in indoor recreation centres in the 1990s and there was a general decrease in indoor court sport participation across SA, which was echoed in ABS stats across Australia at the time. I had decreasing involvement through the 2000s in a couple of rec centres and that trend continued in them, largely losing numbers to the indoor exercise (gym) market. I don't know if that's changed in the last 10 years.