Yeah, you can definately use this idea for a future game, I definately see potential in it. However, in order to be a true sandbox game, you must be able to create something, and show it off. This game has a few limitations.
not bound to layout
title page (home screen)
character is able to place blocks
This would make a great update, reply to my comment with the updated capx attached, and i will rate it 5 stars and comment :)