While tennis will always be popular and a draw card in Australia (it helps having a Grand Slam), also acknowledging there was another record attendance and TV audiences stable…
I agree with @OnAir that the ‘peak interest period’ (i.e.) now and the last 20 years is gradually fading away, as the ‘changing of the guard’ as uttered by McEnroe starts creeping in.
I also think an interesting point, in terms of Australian TV audiences, was how last year’s final plummeted around 1m viewers, even though it still had Federer and went 5 sets (albeit not as fever pitch as with Nadal). It perhaps also shows how well this year’s final just played actually did (around 1.6m close to last year), even though it was a very one sided thrashing.
So what I’m saying is I think it’ll take an Australian to make the final to see peak interest again (Kyrgios? Barty? de Minaur?) as clearly even the biggest names are no longer the draw cards they omce were.