This is so cool, I have been dreaming about something like this 
Few ideas / wishlist:
- Can you make it auto reload the preview when user make changes to the Form?
- Add another preview button to preview the Form with latest Web Forms
- I see you are using
handsontable, its license seams quite restrictive to me. If you could replace it with something with more liberal licence like Jspreadsheet-ce then this thing can become something big down the road. Maybe becomes part of Central - not promising anything but I would love this to be inside Central and primary way to design/edit Forms.