And scince we don't have tilt and we don't have a stroke by just touching the screen with the pen to have a ligth stroke
(we have to press harder to have a stroke and just touching the screen with the pen don't make a stroke unlike other graphic tablet) I think you should make a surface pro 4 pen+ that add tilt,a second button,and is much sensitive to draw stroke by just touching
the screen with it
And I forgot after adding smoothing and calibration and others to the pen software you should add an option to let us choose what the pen button do and what pressing on the eraser do
for exemple if I want that presing the eraser undo the latest stroke and that presing on the pen button is like pressing on Shift on photoshop
You should also add profile so depending of wich program we are using it change the profile
then we should be able to save and load those profiles(like on wacom software)
And btw if you are doing a surface pro 4 pen + the eraser should have pressure sensitivity as well
and if possible those who already have a surface pro 4 pen should pay less to get the pro + one by giving it back