Let's take a look at the Blocks and Layout initiative Prototypes to give feedback on the ways these new UIs can be implemented for Drupal 8.
Here is the latest Prototype:
(click "Add a Page" to get to the most important part of the UI, namely how to pick a layout for your page during the creation process)
My initial impression is that this approach can be easily accessible because it is forms-based. It does not use any drag-n-drop interaction at all.
Is that the right approach? If we have feedback, it's good to provide that early in the design cycle.