As a person who has been using pen / stylus / touchscreen computers for a very long while, I'd like to weigh in:
- touch is becoming ubiquitous as was noted
- there are also tablet computers which have active digitizers / styluses which afford pressure-sensitive input --- Inkscape works well on these as is and is quite nice to draw w/ (at least for people accustomed to Bezier vector drawing programs) --- this is not limited to just graphics tablets for desktop computers or Wacom Cintiq units
- simplifying the interface and affording more user control over size / placement of controls and allowing some on-screen modifiers would go a long way towards making Inkscape more usable w/ tablets, whether touch or active digitizer --- I have to run a small button bar utility on my Toshiba Encore 2 Write 10 which provides Alt/Shift/Ctrl/Space/Tab/Enter keys.
Flash is descended from Futurewave Smartsketch, a drawing program which was originally designed for use w/ tablet computers, so examining it may afford some useful ideas.