They won't do it for a couple reasons:
A 4:3 ratio is not really appropriate on a phone like it is on a tablet
The resolution is not an even multiplier of the existing iPhone resolution, developers will have to develop for it as if it's a totally separate device
If they make the screen bigger, they'll probably just keep the current resolution. It won't be quite as dense as the original iPhone, but it'll be around 300 which is good enough to be considered retina. Most people probably wouldn't even be able to tell the clarity difference.
The resolution is not the problem. It is the aspect ratio change that would be the real problem.