All of the hardware suggestions in these types of threads eventually fall into the "impossible" or "completely impractical" categories.
Cost, energy efficiency--these are things end-users who add lists here and elsewhere never think about. How much would a Wacom active digitizer cost and how much power would it need? Those are the two reasons why I'm dubious about MS adding an active digitizer+pen to the RT line, but would rather prefer they enable the Tegra4+ DirectStylus. Then of course, the distinguishing between lines.
Then some people are still whining about a chassis silo for the Pro pen, when there are technical arguments against that: requires a thinner, less comfortable pen; requires a longer chassis which means heavier and bulkier. Seriously, this is not rocket science to figure out on your own.
People ask for thinner, but that's impossible with the Surface 2. MS has already said the Surface will keep the USB port. Lighter? Sure, if we get rid of the metal chassis and Gorilla glass, things I'm not willing to give up.
Then for the Surface Pro line, if you ask for thinner and a faster processor, where will the heat go and how much space is left for the other components? If you want to add GPS/LTE, where do those modules go and how much would it add to the cost?
Practically speaking, where MS has the most room for improvement is indeed the OS. Maybe some further super-engineering-patent-wizardry for the kickstand.