I actually think the logistics of it aren't too hard.
Enlarge Goschs oval to be similar to MCG and build gym, admin, etc on carpark F, which is between AAMI and Goschs Paddock grassland. Three story building should be sufficient on such a large space. Four story if underground car parking is included. Numbers of staff/players/FD at AFL clubs will be shrunk dramatically soon.
We already use the grassland around the oval for rehab group, it's possible some Aussie rules posts could be put up at one end, even if it's not a defined oval. It's a big space which is not protected parkland and IMO underused. Take down a few trees trees to enlarge the current oval, shift the internal footpath, put in some decent landscaping to appease Council and resurface the oval up to AFL standard.
The hard part of all this is finding the money, which will be near impossible for the next 10 years. It's also no certainty that the other sporting clubs will survive and/or stay at AAMI