Aluminium and magnesium are quite light so that should not be a problem - especially not if the space previously taken up by those hot parts is filled by using a larger battery. The think may weigh 2kg instead of 1.5kg and it may be a few mm thicker. It also should have fewer problems in getting rid of heat (which translates to better performance) and the autonomy should be significantly increased due to that larger battery. I'd choose increased autonomy and performance over a lighter and thinner laptop any time.