I agree, some modeling techniques will have to be utilized. The issue of non-radial motion and earth referenced real time position requires some presuppositions. More than likely a non-radial expansion utilizing red-shift for distance traveled, speed and acceleration. But even more detail will be needed to calculate say a 1 billion ly galaxy, where is it now? GR and SR would say it doesn't matter because the speed of light and gravity are the same and so for any practical or physics related issue this is all that matters because what we see now is how we are affected now. I think this is a terrible mistake and does not allow us to understand or explore any Gross geometric dynamics that the Universe may or may not display.