Yola, Weebly, SquareSpace, etc. etc. etc. I know you've seen a drag and drop builder somewhere. Reality is that this is a multi-trillion dollar market that will always have room for another market.
I tried to build this at one time, before I had the experience to really pull it off. I think myself, a good designer, and another programmer could build a better, simplified proof of concept over a weekend:
The market has changed and now there is a big focus on mobile, and my thoughts on how a web builder should work have changed - but other than that - I believe there is still opportunity here.