The tab looks to be a way for them to share tentative plans for features they are working on without committing to a specific version or ship date. The tab features a prominent disclaimer:

This board reflects some of our current Unreal Engine development paths and we intend to update it regularly. This is not a commitment on which release or date any features could ship. All plans are tentative and subject to change without notice.

There's a lot of interesting stuff here, like a next-generation terrain solution, UMG style sheets, and a design overhaul for the conten browser.

Take a look for yourself. Worth bookmarking!