The A330-900neo is not a good fit for CX's short haul network because it is heavier than the A330ceo. The neo's sweet spot is longer medium-long haul routes where the A350 is even stronger again. The 787 may be a better fit for CX short haul but I'm not sure how the numbers would stack up taking into account capex vs the "intelligent misuse" approach of just deploying surplus long haul aircraft on short haul routes when not operating long haul. I'm also not sure if CX has enough long haul frames for this approach taking into account the A350s on order net of 330/77W retirements. There's also the possibility of future performance enhancements to the A350 (including weight reduction, RR ultrafan if and when it materialises etc) to make them better short-haul performers.