First, I'm glad to see that for the developers at least, accessibility is definitely a priority while building this. That's encouraging. Hopefully, should the worst case senario happen, (Matt deciding that WCAG holds something up and so it has to be thrown out), the developers have some ammo. Second, I'm rooting for drag and drop to be added because of ... wait for it ... accessibility. For right now, with the current block-moving functionality, I and others like me who use only a keyboard have an advantage over everyone else. We're used to interfaces like this, where you have to click arrows to move things. But for mouse users, that's not something they're used to, so it means that they have to conform their use patterns to the tech and not the other way around. In order for this to be accessible, it has to allow, (as much as possible), for users to operate it according to their choice, instead of being made to conform to the technology. That applies just as much to mouse users as much as it does to users with disabilities. I think it would be incredible if WordPress builds a page builder that anyone can use, regardless of whether or not they have a disability. It would be the first of its kind.