Regardless of whether the EULA/ToS has legal teeth or not, there's a surefire way for a theoretical addon author to avoid it - don't buy/subscribe to WoW. If you've never entered into any contract with Blizzard, there's no way any clause of those contracts can affect you, but there's nothing stopping you from writing an addon that can run in WoW (admittedly, it'd make debugging a pain, but we can ignore that for the purposes of a thought experiment; just assume our theoretical addon author is perfect and never writes bugs). WoW addons, after all, are just Lua code written to a publicly-documented API; you could write one with nothing more than the Lua docs and one of the various API references available (either online at WoWWiki or wowprogramming.com, or a dead tree version).
An argument can be made that all addons are derivative work from blizz using their API to function.
Use of an API doesn't constitute creation of a derivative work (if it did, there'd be no way for anyone to create non-GPL software that ran on Linux, for example).
This whole policy seems massively overreaching, if you ask me. You could theoretically create an addon that doesn't even have a hard dependency on WoW (just use the base lua libs, etc). You couldn't do much of interest, but that's beside the point (well, not to end-users, anyway).
The main lua source file for such an addon would undoubtedly be your own copyright, and thus you have the right to do whatever you want with it, license it however you like, and charge whatever you care for it. Does adding a .toc file to the distribution now instantly hand your copyrights over to Blizzard, and give them the right to dictate your licensing terms?