Prior to launch one of the A380 configuration concepts was to use some of the unusable cargo hold space for pax amenities. VS was going to have a gym, running track and casino in the basement, for example -- until they cancelled their A380 orders
Maybe QF has plans for an F basement with special amenities. The F suite weight and size probably was a consideration in selecting lower deck over upper, it has a lot more flexibility in configuration. It is amazing how heavy the F suites are.