For me, I would change a few things like allowing druids paws to scale and allowing chance on hit procs and so on.
Also, I would also create level 70 heroic versions of all the old instances and raids with scaled gear equivalents to expand on the endgame and allow more gear possibilities and such. The theory crafters would have fun with that.
Have plenty of others I had thought of, made a post about it a while back, but thinking on it, I would probably change some of them now. But here they are.
Extended AFK, later man and Happy New Year.