A first boost to the A330 program was for sure the A330-200 with the longer range and exceptional economics. The further developments of the A330-300, which led to a longer range thanks to more MTOW was a second boost, above all in the last two years. Remember, that the first A330-300 had a MTOW of 217t while now the A330-300 is offered in a 233t version and apparently will be offered even in a 240t version.
Perhaps, one day the A330-300 will replace the A340-300, leaving the (ultra) long range high capacity market to the A340-500/600. But this would need more development costs (new wing, engines, ...) and would be a break in Airbus' strategy, according to which, twins are good for routes up to 5500nm and quads more economical on routes longer than 5500nm.
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