From what I've read, both Nvidia and AMD have made great strides in TDP efficiencies with their latest generation of GPUs. I think Apple would do well to adapt these GPUs ASAP. Whether they choose to go with AMD or Nvidia, it will be huge steps in the right direction.
If you can live with using the built-in HD 530 for now, do so until Apple and/or Nvidia give us indications of what will be supported.