And let's not forget that while everyone may not want a custom design for their sites, there are a lot of people out there that don't want to maintain their own sites, and would rather pay someone else to do so. When that happens, what's the difference between building something custom vs. WordPress and a nice theme vs. SquareSpace and their offerings? The value isn't the deliverable as much as it's the comfort in knowing your web stuff is taken care of and you don't have to deal with it.
I suppose at that point you're not talking about "web design" per se, but a "small web business." But I'm OK with that. Additionally, there is still room with those options to provide value more than just set-up and maintain. Writing good content and creating good IA is still a challenge for all of those products. To me, all of these things are part of being a small web shop, and from what I can see are things that won't be going away or automated any time soon.
Although the once automated, we'll essentially have robots (creating content) fighting robots (search engine spiders), which I think is something we can all agree on as being fun to watch with a drink in hand.