Check out the NEW Nintendo DS called the DSi. It has 2 cameras, 12% thinner than DS Lite, bigger screens, support for SD cards and music playback. Will the R4 work on it? I have no idea. Probabaly Nintendo will do a hardware lock of some kind. Oh, the Nintendo DSi also has NO GBA slot.
DSi vs DS Lite comparison: here. Click the rightmost menu item.