Front end Drag and drop website builder/ software for Wordpress

Hi I am looking to create a plugin or theme (or even a web based tool that you just need to then publish to Wordpress) that enables you to edit a wordpress page from the front end with almost a grid like set up so that you can place elements anywhere and even ontop of each other It is important to watch the video below as I am NOT after a block set up like visual composer but looking for a grid set up like in Unbounce or instapage as can be seen in the video below NOTE - I am happy for it to be a small extension that allows you to edit an existing theme as i'm not too fussed about the how and am more concerned with the functionality/ getting the end result I want the functionality to be exactly the same as Unbounce or instapage does in this video but it needs to be able to be hosted on Wordpress so that you dont lose the site should you switch providers [login to view URL] Some key features - the grid like (NOT blocks as most plugins are) - it needs to be editable simply using the front page - there are no restrictions on where you can drop elements on the page - must be able to create new themes and templates OR edit existing themes and templates for example it can be a plugin which works with a WP theme to make editing it simpler (like visual composer in the sense that you can use it to edit any WP theme) I would prefer to go with an add on to something that already exists so if you can do that then fine but if not a new piece of software is fine I am looking for speed and cost efficiency as if it works well I may develop it into a SAAS and would need you to work on that too