Making a Android version of HD Edit is no problem at all, if you have Andorid 3.x or higher. It comes with a USB API. There is no need for a driver. You can simply talk to the USB Endpoint. I have already done something similar using libusb on my PC. HD Edit uses SysEx commands to communicate with the POD, but simple things like changing the presets/knob positions work with standard MIDI PC/CC messages. If Line6 would provide any documention for the SysEx command, doing it would be a trivial job, but since there is no help from Line6 you would have to reverese engineer all the SysEx stuff from the existing HD Edit version.

Here is my simple and still very ugly ;-) test code (this has the appropriate Vendor/Device ids for a POD HD 400):

public class PODMidiTest {
    public static void main(String[] args) {
        byte[] data = new byte[] {(byte) 0xC0, 0x04};
        byte[] inData = new byte[8];

        Device dev = USB.getDevice((short) 0xe41, (short) 0x5058);
        try {
            dev.open(1, 0, 5);
            int res = dev.writeInterrupt(0x03, data, data.length, 2000, false);
            System.out.println(res);
            res = dev.readInterrupt(0x84, inData, 8, 2000, false);
            System.out.println(res);
            System.out.println(Arrays.toString(inData));
            dev.close();
        } catch (USBException e) {
            e.printStackTrace();
        }
    }
}

It is less about audio and performance and more about convenience of editing. 

I don't think my world would end if I could not edit presets on the Pod with my wife's tablet (pried from her cold, dead hand btw)  but It might enhance my life in some small way if I could tweak on the droid.  I am more likely to tote a tablet around than a laptop.  

Other people have aspirations towards using a Tablet in their performance.