I would like to suggest that future versions of Scrivener feature an option to cover all but one line in a document like one might do with two pieces of paper when proof reading. This would allow someone to read/edit line by line and force them to focus on one line at a time.
A user could activate the feature and use the up and down arrows to choose which line is visible. When activated, the program could cover all but the line that contains the cursor.
If my meaning is unclear, see the following webpage:
The practice that I’m trying to recreate is mentioned under the heading “When You Proofread.” It is the third bullet-point.