Here are some things in mine that I've found useful but don't see here (/ might have missed) and could be food for thought (presumably some of these are just NYI but noting them regardless): [edit: a couple of these things are already noted at https://github.com/GraphiteEditor/Graphite/issues/1870]
- shift+G/R/S for setting handle mode (bent, colinear, and colinear+equidistant respectively) works out quite intuitively; mode can be displayed as a different icon on the point (square for bent, rectangle aligned to angle for colinear, and circle for equidistant is what I use; circle is somewhat questionable but my handles have arrow tips)
- while holding just a handle, set the rotation/scale anchor point to its point
- allow both rotate and scale at the same time (maybe never useful but I still did it. ¯\_(ツ)_/¯)
- while rotating/scaling, some shortcut for setting the anchor point (esp. snapped to an element representing the rotational center of a symmetric design)
- middle-mouse-dragging while holding an element should ignore the delta mouse movement during the movement
- I draw visual indicators of the current r/g/s accumulated action (g: a line from the starting mouse position in the canvas to where it'd be dragged to; s: line from the anchor point through the current and original mouse position with different colors (i.e. the ratio of the color lengths is the ratio of scaling); r: lines from the anchor to original & current mouse position, with an arc in between (very busy-looking, don't quite like it))
- some actions - cut a path into two (a thing I don't have but have wanted is drag-selecting to cut into three), snapping to existing points if near enough; and another to join paths if two end-points are selected; and select all linked to current selection