Yes, you are correct, but eventually even awareness of the body is dropped as well, as the mind is turned on to the mind. Of course there will always be a starting point, or point of focus even when beginning "just sitting". I imagine only meditation masters can sit on the cushion and plunge into pure awareness. I have just personally never come across any Therevadin teachers who have emphasised this sort of practice or took it to a level that practitioners of shikantaza have, that I know of.
The concept of "just sitting" has always been very intriguing to me and being a practicing Therevadin and not a zen practitioner, I did not think this sort of practice was open to me. Of course I can practice whatever I want, but I do not want to mix traditions or practices, though I do admire the old zen masters and their texts. So naturally, coming across the concept of sitting in "choiceless awareness" within Therevadin Buddhism have set the wheels rolling for me.