You only need to store the data until you can upload it, which might not be that long if the car has an internet connection. Furthermore I assume not all parts

You only need to store the data until you can upload it, which might not be that long if the car has an internet connection. Furthermore I assume not all parts of that data is equally valuable. If this is raw data coming from sensors I think it is fair to assume that a significant part is noise that can be discarded. So I would assume that even though you are probably unable to store 1GB/s of data - today at least - you might still be able to store the interesting parts and use those.