Goodnotes 6 is an awesome tool for drawing however these 5 options could be very useful to say the least, wether it’s for drawing or for being precise
(some are already suggested but maybe not in the way that follows)
These includes:

1) A length lasso option that measures any straight segment
(in relation to the page format, it shows the real life measurements)

2) A new compass tool, better that the original: with custom traits, adjustable length and a GUI showing the angle at which the arc is being drawn

3) A shape lasso option that turns any closed shape into a regular form
(only works with polygons)

4) A mirror option in the moving mode (previously selected with lasso)

5) A goniometer showing the angle at any given point referred to an original orientation independent form the page itself.