The way most blame modes work is that they annotate the entire file up from front and puts the commiter name, hash, data for each line side by side with the file contents which requires a very wide display and is often not helpful anyway. 

Instead, I think a mode where you have the file in one pane above another pane that shows the commit msg and the diff would work better. Sort-of like the default gitg arrangement, but with a file view in the top pane instead of revision history. As you move the cursor up and down in the file, the lower pane updates the commit to display the commit that last touched the line the cursor is on.