this post will contains some suggestions which have no link between them.
-Firstly, i think it could be great to have something which allows us to follow news from w3schools "easily, something like a page where we could see the last update in a single line.
02/03/2018 Update "How to" section
01/30/2018 Add php tutorial (server side)
In fact, the website become "big", then it could be an asset.
-Secondly, i see more and more websites which have a functionnality to switch the theme (to a night theme) by clicking on one button (in their navbar) and the change is done on the whole website . This featur could get its place in "the How to" section.
-To finish, this last idea is probably out of the main content of w3schools, but maybe Java could get its place like Node.js in the server side section although Java does not necessarily have this main purpose. (of course this add should only approach the server side).