I'm going to say no for any type of content creation tool for making your own worlds from scratch. The same reason Microsoft didn't allow similar tools for existing games like The Elder Scrolls for example. Microsoft considers them mods which they just don't allow. I want to say the reason is all about money. With the right tools the community could certainly create fantastic content, which being free, would hurt their chances of making more money on DLC they make. A sad but very reasonable truth from a business perspective. Now as for a forge type editor, sure. Simple map editors that lets you use existing objects to create maps is much different. Historically for Halo, some forge maps were splendid works, but they were not entirely new maps.