That's another issue they can't figure out - when to play the AFLW season. You raise a good point that the MCG isn't available unless it lines up with the AFL season (but that would make finals schedules a real challenge to fit 8 finals in wk 1).If it stays in the current timeslot the MCG will be being used by cricket.
So it'll be Marvel
That's probably why they let it float now: Optus and Adelaide Oval fit more than Marvel and the Gabba and SCG are pretty close.