I always thought it would be cool to see a huge NM suddenly land in one of the lower level zones so new players could actually see one. As cool as it would be to have it suddenly start tearing the place up and killing everything in sight until a large group of people could mobilise on it, I don't know if SE could do it. I think a lot of lower players would be angry if it swooped in a started one shotting them, I'm sure many would still like to see something like this though, have to make it a pretty rare occurrence though so when it did happen it would be pretty special.