They need to refine the technology to the point where it won't add significant weight to the device. There's also the screen distortion issue. The Air 2 just seems too flimsy to me at the moment for something like that. I fear the weight gain from 3D touch on the regular sized iPad would be quite substantial. But I could be wrong and I certainly wouldn't mind being wrong on that! Personally, I think it would be far easier to add Apple Pencil support and I would frankly much rather have that than 3D touch at the moment.
As for Rose gold? Sure... bring it. But I'm done with white bezels, so there's really only one choice for me. If only they would make gold with black bezels. The gold Apple Watch Sport looks stunning because of it.