Maybe a level editor and RC add-on which shows the line that you are currently in as you are scripting. Maybe in like a box on one of the sides or so.
Example:
NPC Code:
//#CLIENTSIDE <--While typing this it would read: Line 1
if (created) <--While typing this it would read: Line 2
{ <--While typing this it would read: Line 3
actions; <--While typing this it would read: Line 4
} <--While typing this it would read: Line 5
Also: Possibly an add-on where everything added (scripted) to/on NC is given a line count number on the side of it.
Would be useful for reading errors given by the GS2 script compiler and would really just make things easier for servers that need to fix certain parts of scripts and they would be able to describe which part is needed fixing by giving the line count (example: Lines 20 through 26) to the NAT(s) of the server.