I don't think the current implementations using 4 wires can ever be converted to multitouch. Since we are only getting the resistance between X, Y I can't imagine a possibility to actually identify multiple inputs without a major hardware change. I believe the basic working principle of the current touchscreen is that you read the X and Y resistance quite similar to two variable resistors and you get a coordinate on the screen. Min and Max can be determined using the calibration and pre-programmed in the factory. No amount of software will make it multitouch since it won't have the necessary data to work with.