I'd imagine that if Apple does in fact change the screen size of the iPhone, they will most likely release a matching iPod Touch, especially if there is a change in aspect ratio. I can imagine that once that new ratio has become the norm, there won't be many app developers continuing to write apps using the original ratio, and that would mean that the 4G would be left in the dust. So if there is a change to the ratio, I think Apple would almost certainly change the touch to match, but I don't think they'll necessarily release a new one until then.