Crunching some numbers (from wiki and elsewhere)
B787-9
MTOW 254.011 kg
MZFW 181,437 kg
MLW 181,437 kg
OEW 128,850 kg
Fuel capacity 101,456 kg
Qantas configuration 42J/28W/166Y = 236 pax = ~24 tonnes inc bags
Average burn assumed 4.5 tonnes/hour
17 hour flight = 76.5 tonnes + reportedly about 7.5 tonnes remaining = 84 tonnes in tank (might be 3% or so more with contingency fuel, let's say 87 tonnes).
So MTOW-Fuel load = 254 - 87= max allowable ZFW of 167 tonnes
OEW + full pax load = 128.9 + 24 tonnes = 152.9 tonnes
=> freight capacity = 14.1 tonnes (or less depending on actual OEW subject to QF fit out)
Doesn't sound like any pax limitation needed to me