Dear Sir, first of all thank you for such helpful website. Now as w3css framework is very useful and easy to implement. I want to suggest if following modification is possible in your new version of w3css.
1. Menu structure with ul and li elements rather than using only a tags. That will be easily implementable in WordPress default menu structure and having drop-down facility also available.
2. Menu items are being used 2 times for making it responsive rather it should use items only single time.