I've been pondering with functionality to best use devices having both stylus and touchscreen. I did some experiments with normal xournal, so that stylus could be used for canvas and touchscreen only on the menus. This would enable user to put her hand on the screen while using a stylus to draw on canvas - just like one draws on paper. This of course requires tablet with separate stylus & touchscreen, like Samsung Series 7 Slate, which has both Wacom & capacitive touchscreen.
I did some experiments with code, but limitations of GTK2 made it rather difficult. In GTK3 there is better input device management, which should enable this kind of functionality - and all other possible new use cases including different kind on input devices.
I checked out xournal++ which would be definitely the way to go, but I'm wondering whether there any plans moving to GTK3?