Information about messing with opcodes:
http://www.showeq.net/forums/showthread.php?t=5314
I'm sure the place to start would be making sure the login server stuff works correctly (easy enough), then start piecing together everything else until stuff starts working. Heck, there's already code to support a patch_Anniversary.conf file in common/patches (although I'm not sure to what extent). The harder stuff will come when packet structures start changing (like the profile & spawn structures?).
Of course, we can't really sniff packets from Live, since I'm sure that stuff's changed... However, some
older ShowEQ files might help quite a bit.
Just some thoughts if someone wants to look into this...