We also have this issue and would love to know if you found any solutions.
We want to "upgrade" the AEM float grid to use flexbox to take advantage of all the layout power it opens up. We haven't spent too much time on it yet, but our first attempt was to change the grid.less files to display: flex. The main issue that had was in responsive authoring and parsys. The "drag components" section is shifted to the right and is difficult to adjust the layout.
Any thoughts or help will be greatly appreciated! It's unfortunate that Adobe is so far behind the curve and still using floats...very disappointing.
