Not such a hot idea...
Hi Nipper
Super-heated oxygen would be super-reactive against the engine components. Also if it's too hot it won't react against the fuel - both will be ionised with no net gain in energy.
The "light-bulb" system heats the working fluid via UV emitted from the 25,000 K glowing core, avoiding vaporising its components because the encapsulation is UV transparent and the gas-core vortex avoids physical contact with the containment vessel. The vortex is manipulated by gas-jets and (possibly) magnetic fields.
Adam