What can't "scripting" do "properly"? What do you define "properly" as? Properly is definitely not using a workaround event like on newline to capture text that was triggered from other sources (on text, action, raw).
You also get into consistency issues of "does /echo trigger an event"? and if it does, you wouldn't be able to use echo's (to the target window) in an on newline event, it would just recurse infinitely.
And if you're just trying to capture non /echo'd text, well then you can already do it with the proper events. If you can't, then you should make a feature suggestion for that specific missing event.. not all of them together. That's not "proper" scripting, in my opinion.
Just to go a little further.. incoming text into a window is rarely just a "line". It has extra important information that goes along with it (on text has $fulladdress, $nick, etc., on op has $opnick, ...) You can't just generalize this differing information into a "line"- they are distinct events and you handle them differently too.
How would you even use an event like this? How would you differentiate the "lines"? What, would you check that "sets mode: " is in $1- to tell if its a mode event? If that's what you were thinking, then this explains why this event would be a horrible idea.
