When EK started to Australia, they did not do non stop between DXB and MEL. A340-500s had not been built then. They happily operated with a stop in SIN, and even now one of the of the daily flights from MEL operates with a stop in SIN, and one of the daily flights from SYD operates through BKK. SO...if EK wants to start building the market from ADL, they do not have to do non stops from ADL. I note that ADL does not have direct flights to BKK, whereas it has flights to SIN, KUL and HKG, so EK could offer holidays in Thailand until they decide ADL can support non stops.
ADL may be a third of the size of SYD and MEL, but it still has people who want to travel to the Middle East, Southern Europe, and many other places they cannot fly to on Oneworld carriers.
EK could even annoy AirNZ and QF by extending ADL to AKL. They would be the only airline offering a widebody, and they would offer a bit more food than Air NZ.