the high customization of the UI is one of the reasons why I still play wow (besides the fact it is still fun for me and I have a lot of friends there and so on). If wow would be suddenly zerp addons, I highly doubt that I would continue playing.
But luckily this is not going to happen. too many people would quit because of that, there would not be any logical reason behind such a decision after 9? years WITH addons.
even if there would be a wow2, I highly doubt that they'd remove addon support. the community itself and the addon community is just too big to justify such a decision.