Do you have any idea of whether or not addons will be enabled on Classic? What API they will be using?
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
I'm sure you saw the blog post, but this is all we know so far. I would assume the API would be the same, just adjusted so that objects dealing with specific stuff like garrisons or guild bank would simply be missing. Core stuff like handling frames and textures or all the new mixins would probably be there.