I honestly doubt we will get a full blown terrain editor for Forge, as no one would buy the DLC if this was true. Perhaps we could build our own vehicles and weapons similar to some of the mods. There could be separate sections of objects just used to build the vehicles with. You could start from scratch or off another vehicle.
The idea is good, but people would just make too big and powerful vehicles/weapons, therefor, this would never be used for MP, therefor, it will probably not happen. but like I said, the idea is pretty fun 
343, hire this man.
> 343, hire this man.
> > 343, hire this man.
Done
> > > 343, hire this man.
>
> Done
Well that was fast.
Wait a minute…
vehicles yes, weapons no
the weapons sandbox is big enough, and we don’t need any more of them
vehicles on the other hand…
I also would like some of this, 
1. Far Cry 2 vs. Halo Forge 2.0
I’ve seen many people on this forum, want a Far Cry 2 map editor. Here is what it looks like.
What really impressed me was around the beginning. The mountains, texture and the weather, time. That really knocked me off guard. But, I don’t want that exactly. I want to still be able to Forge pieces like normal. With Far Cry 2, I don’t see very much, uniqueness.
2. The Forge Moniter’s transportation.
I love this little guy. But one thing that must be done, is to get around the map faster. I remember (I still do it) dying and having to re-spawn on the other side of the map. It sure got tiresome What I was thinking is this. Teleportation. Remember how in Halo: CE, Guilty Spark could teleport anywhere in the Installation? What if you could teleport in Forge 3.0. I was thinking that you click a certain button or whatever and it will show you a bird’s-eye view of the map, then a cursor will move according to your left analog stick. Then you click A, a voilà! You teleported.
3. Moniter’s Rampancy.
Our Forge friend is very nice. A little too nice. I think the Forge Moniter should be able to kick some -Yoink!-. He should have a laser, similar to the one in Halo 3, not in Halo: Reach. (Focus Rifle Glitch) I know this has been said, but I can’t stand this little guy being pushed around.
4. Forge Moniters Demise.
Have you ever been building something, and you out an object somewhere out the ordinary? Than all of a sudden, You crap out, you go underground, you die, you go to the other side of the map, and then die. I think 343 should fix that because it really got annoying. Now I have a way to fix that. The Moniter shouldn’t move unless you move the piece somewhere else.
5. ???
6. Profit.