Haven't been there for about six weeks but judging by the e-mail I just got, it seems they decided not to rebuild P1 (at least not at the moment), but instead just pave it* and call it "P1 Prime Park", an open-air carpark.
https://prebook.sydneyairport.com.au...-park-parking/
I'm kind of both surprised and not surprised at the same time.
* Okay yes I'm being a bit flippant, presumably there's a bunch of civil work with drainage and lighting and car park systems et. al., but that's what makes it surprising as this clearly is not a long term solution and clearly not "redevelopment of the site as a catalyst for improving the experience for customers and operators in the precinct".