Interesting rumour. I seriously doubt the veracity, especially the dual livery, but I've been wrong before. Anyway, my interest was piqued so.... A certain flight plan I have on my ipad tells me:
200LR flying an air distance of 7100nm at max ZFW will fly for about 15 hours and burn about 115 tonnes of fuel. TOW of about 330t (max is 343t) That was on an August day from DXB so summer departures from DFW wouldn't be a problem.
The Don is correct about seating numbers so that would allow for a significant amount of freight. I think DFW-SYD is a bit further than 7100nm but shouldn't pose too much of a problem.
Of course the 777 is a heap of sh*t. Just ask Geoff (and The Don
)