In gerrit 2.5 line numbers in side-by-side view was moved to the right side. This soliuion:
* made harder to distinguish visually whether block of blank lines is part of the file (and should be pointed out in review) or just result of side-by-side diff when left file contains more lines
* made a bit harder to visually identify folded lines in the right side file
Displaying line numbers on the left/right side of the right file could be an option in the user preferences. I feel more comfortable doing review when I see immediately which part of the right side code is the real part of the reviewed file, and which is not.