When AAMI Park was built, to their credit, the Victorian Government spent the money to build the foundations of the ground so it could be expanded to 50K without needing a whole tear down & rebuild.
That said, even though the ground could be expanded, it would be a hard business case to justify at the moment.
Firstly none of the tenants are filling the ground regularly. The Storm averaged just under 20K, but only had 2 sell outs from its 11 matches.
Victory averaged 11,300 last A-League season, City 8,400 and then Western United I'm pretty sure have moved out completely & the Melbourne Rebels are dead.
Secondly, from a big event perspective, the NRL, Rugby Australia & World Rugby have all shown that if they are going to take big events to Victoria, they are more than happy playing at Docklands or the MCG.
It's only Football (Soccer) that has ever pushed back and then it is only for events like the World Cup or Asian Cup. The Matildas played at Docklands as recently as February this year for their Olympic Qualifiers and the Socceroos last year.
If you're current tenants aren't pushing capacity and the only rectangular sports event that enforces it isn't something we're even guaranteed to win (FIFA Men's World Cup) or unlikely to get again soon (FIFA Women's World Cup, Asian Cup), it is a hard push, especially in the current economic conditions.