I hate to be the one to come in a piss on everyones parade, but a lot of the ideas or wants are just too "out of the ballpark".
I see a lot of talk about AI. Firstly, you have to understand that a thing called "triggers", "zones" and "pathfinding" is needed to make AI function properly. There is a reason why AI was on Installation 01, and it wasn't because it was easy to do. The ODST bipeds were specifically compiled into that map for a scenario file for players using Chief. In order to allow any kind of AI or NPC character, we would have to be able to edit/write/rewrite certain fields only accessable to the core scenario_file tag. As many do not know, the edits we make in Forge are simple top layer variant settings, and not core .map edits.
The other thing that bothers me, is the need for a terrain editor. Terrain just like any or most geometry in halo is a BSP. A BSP has collision (coll) and physics (phmo) compiled and assigned to each plane/face/edge/vertice when the map level mesh is compiled into a proper sbsp tag. Editing the terrain would require us the ability to recompile physics and collision on the level mesh, which aint happening on a console. At least not to any true working degree.
While I agree that things like this would be cool, it just isn't going to happen. If it were possible to do these things, we would have seen some of it in Halo 4. And for the record, the crappy lighting thing they tried to pass off as groundbreaking or next-gen....it sucked. It was just a form of using prebaked lighting schemas to simulate actual shadow casting, and most of the lighting shiz had to do with first person camera, not environmental lighting.