We-e-ell, there's strong expectations that there will be at the very least a front-camera so they can add iPod touches to the roster of Facetime-compatable devices, but they're pretty small so I don't think it will make the device any thicker. I think one of the big reasons for the new flat back on the iPhone was to make it thicker at the top to house the new rear camera.
Will the next generation of iPod Touch be the same shape as the iPhone 4? That'll sell me. I don't like the curved back of the current generation iPod Touch.