I already said that if you bring a different inertial frame into the equation then you have causality problems. That requires a third frame of reference interacting with the first two!
I don't follow this at all. The traveler and the earth are two separate frames of reference. Nothing more is required to generate the effects I've been talking about. (If the hypotheticallly instantaneous transmission system makes them both into a single frame of reference, then you'll never have a 3d reference frame, because it too will be in instantaneous communications with the others.)