Island - from what the scuttlebut is on the surface - the stripped down version will be 1.4 lbs (sans keyboard) exactly what an iPad weighs...
And if you want to talk case - magnesium- really - wait till that first battery catches fire...
Again - it will be months before we see one on the shelf - or who knows it might be vaporware once Microsoft's hardware partners start pounding on them.
And you should try the prime - it really was an interesting machine.