Not nearly as ridiculous as suggesting Melbourne needs a 50k rectangular stadium. It would never, ever get used. Here is why:
- it would be way too big for Storm games that average 18k, or A League that averages 10k. Or Rebels games that average 8k. The atmosphere would be terrible, and it would be far les profitable for tenant clubs.
- for event games like SOO, Bledisloe, WC qualifiers, etc, they would still be played at the MCG, as 50k is too small. Do you really thing that the NRL would chose a 47k crowd over 87k For an Origin match? No, they will take the extra 40k and extra $4m+ every day of the week. Just like in Sydney the big events are at ACCOR, not SFS, which is only 40% bigger than AAMI.
More likely - if the MCC believe that Australia is a realistic chance to ever host a soccer WC, they will add moveable stands when they rebuild the MCG southern stand around 2030. Unlike every other stadium in Australia, the MCG generates enough revenue to pay for its own redevelopment. If there is an economic benefit from a rectangular mode (such as hosting the WC with 105k) they will do it. Southern Stand first, then the members in 2050.