I’m really excited for Flexbox and the CSS Grid specs. However, you should find what layout systems work best for your audience. Working in the health care system we have to support at least IE8 in most cases, so using flexbox isn’t an option. We are able to use it on internal tools but user facing we tend to still use floats and css grid systems. We force our users to upgrade once they get accepted into our program to a modern version of their browser. We are trying to help influence our audience to use modern browsers but it takes time.