I did, many, many years ago. Back then, Blue Mountains wasn’t even a national park.
To answer your question, yes a koala came and sat on my lap - we visited a park somewhere, I forget the name but it was a tour. The tour guide reprimanded me for having a koala on me (I told him he came and sat on me) and insisted I remove him because of the dangers of its claws (it never hurt me, not even a scratch btw) I feed him & kangaroos food purchased at the site for them. The animals were super friendly at that park. It was an amazing experience considering all the animals were in the wild.
I even went on the Yellow River in Darwin (Northern territories) where the film Crocodile Dundee was filmed. I saw wildlife you only see in Australia on that river.
I could tell you so much more about that country... I had gone backpacking for 6 months and saw everything in Australia except for the west coast (Perth) because I didn’t have enough time to go. (Australia is about the size of the USA)
Indeed, it is a long flight to go there from the USA although I would tell anyone that is interested in going to not think twice and go. Aussies are extremely nice and welcoming. I would not hesitate one bit to return given the opportunity.
G'day mate!