What Iraq needs most is not military support, though certainly of prime importance, Iraq through the PMU and support from Iran has proved that it can handle threats imposed by non-state actors like ISIS, it can also inflict significant damage to state actors, even the US in asymmetric warfare.
Iraq's weakness is, like Iran, economic... it is resource rich but if the US imposes sanctions it can have a tremendous impact.
As such, a Chinese intervention would mostly be an economic one, to the benefit of China itself, which needs both a market and a non-naval road to its target markets as well as resources for its industries.