The Canvas grading scheme selection UI is dangerously bad. The way to OK a selection is at the bottom of one scrollable pane, while the cancel is on an outer scrollable pane. A short video showing this is at
At the very least, make the default popup sizes big enough to show all the buttons at once.
Comments from Instructure
We have some exciting news! This is a project that one of our developers started working on during Hack Week (find out more about Hack Week in Ideas: State of the Union). It is currently in development!