The "Account name" and the "Display Name" seems to be a good idea for me. However, I have some suggestions.
I know that this goes against the "Grand Scheme" of NG. But is it possible to have users decide?
Like I mean that users who want to have a personal page must lock down their names before they can have one. And users who want to be able to change their names not be able to have a personal page. So then now users must decide whether or not to lock down the names for the sake of a personal page.
Also, each user who has their name locked down would have a special indicator (like a boarder or something) so when visiting their profile or replying on the BBS, that other users can see that this name is locked down, and that this name cannot change.
Also, in the case that a locked username wants to change, they would have to be of a certain level and wait 30 days or something before they can do so. If you really wanted to, you could make the users pay a small "fee" in order to have their name changed.
-satisfies everyones needs
-NG becomes less uniform
-User renaming may become a problem
-More alts for people who want both
Another alternative, which probably has been already mentioned, is to have the ID # in the webpage:
So instead of InsertNameHere.newgrounds.com it would become 1234567.newgrounds.com
-Takes away the problem of user name switching
-Doesn't look as nice
But whatever you decide, I won't complain if we have to lock down our names. Just make sure you give us an announcement before you do so.