Oh I don't think they will solely update BC zones for their own sake, and Darkshore and Arathi prove they are very willing to update old world zones to current content.
And in the case of of just creating more zones and updating old ones for an expansion, I do think we could be seeing more of the later in the future; Azuremyst Islands and Quel'thalas have a lot of potential, given that their 1-10 areas could be revamped as starting areas, while Bloodmyst and Ghostlands could become contested areas.
But I do believe a world -if albeit partial- revamp is likely, so that colors my perspective. I just don't think it will be one in one exp like Cata was, and more of updating areas as fitting/make sense for the story.