In the Speedgrader, create an option to toggle rubrics from a vertical view to a horizontal view so that longer rubrics are visible without scrolling.
Most teachers didn’t like using the rubrics because they don’t display well in the Speedgrader. Please consider making a change to the display, so teacher can display rubrics and outcomes that are longer.
When Canvas auto generate rubrics from outcomes, it makes them horizontal, so it makes sense in the space for the rubric in the speedgrader to also be horizontal or at least to have a horizontal version.
With the division of the speedgrader as it is now, the rubric "blocks" a significant portion of the student work, so teachers have to constantly slide the submission left and right to read it or shrink it to such an extent that it is not legible to all but the sharpest eyes.
The idea is for the rubric itself would remain the same, but the viewing pane would take up the bottom of the speedgrader rather than the right side. You could also imagine it as a splitscreen where student work (at page width) is visible on the top with the rubric across the bottom rather than being divided left and right. Teachers would still have to scroll down to see the bottom of the student submission, but that would be preferable to constant left/right scrolling.