Plus all one would have to do is actually use the pen for drawing. It doesn't take an artist actually using it to understand how that's a problem.
Currently the only way to influence it is to delete registry key
[-HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SurfaceHomeButton]
and kill all physical buttons completely.
A) The product hasn't even shipped yet. That may be an option or made into one in an early update.
B) There may be a technical limitation to disabling or rebinding it (e.g. without impacting either other buttons, or the behavior of actual keyboard buttons).