Preview changes in new design tools

I'd like to see a better preview tool in the new design tools that allows you to make changes to the website, including JavaScript etc and see it live without having to publish it to the website for your customers to view the potentially incomplete adjustments. As it stands while the tools are great, if you make changes to anything deeper than the surface adjustments you cannot see them unless they are published which can impact your store. 

This does not necessarily require a test environment, just a live pop up tab or something of the sort which offers proper viewing.