To summarize, what I really want to see out of Halo 5's Forge is a more dynamic Forge.
Dynamic Environments
Previously, the environment in which we Forged in was static. What if we could change that? The ability to change time of day, water level, etc. would allow for a more dynamic environment to Forge in.
Skinned Objects
Each structure piece - and some non-structure pieces - could have several UNSC, Covenant, and Forerunner skins that could be selected. That way you could choose a simple skin for a floor, a more complicated one for a wall, or a complication for an an aesthetic structure. This would also allow for Covenant and Forerunner themed maps, something that was not easily done in Halo 4.
Smaller Pieces and Groups
Traditionally, we had several prebuilt buildings to work with in Forge. These buildings were good, but also somewhat restricive. What if Forgers could design their own buildings using basic building pieces and small, decorative pieces to bring it all together? Then, you could group all these parts together so that they move as one, and save the group to be used again and even upload it to your Fileshare.
Forge World?
A lot of people want to return of Reach's Forge World. Although Forge World was great, I don't think that having one main Forging map is the best approach. Like in Halo 4, there should be several different Forge maps, each with its own environment. A lot of people didn't like this, but I think that if it was tweaked correctly it would be better than the boring and bland Forge World.
Basic is Better
Forge canvasses contain a lot of rocks, trees, and other natural elements. In Halo 5, I think that they should strip all of the natural scenery and just give a basic and blank canvass. Then, Forgers can make their own unique environment.
Natural Objects
Forge Island had trees, which was a HUGE addition to Forge, because now you could create your own vegetation. In Halo 5, Forge should include lots of trees, bushes, rocks, etc. to create a unique environment and set your map apart.
Other
A custom powerup Ordinance drop
More visual effects, and add visual effects to trait zones
Buttons, levers, switches, and other activators
A better system for linear style maps
More Gadgets!
Coordinate increments decreased, precision editing
(Not technically Forge) A gametype category for non-traditional (miningames) games (like Haloball in Reach)
343, please try to add some of these!
Community, please tell me what you think (and please don't hate)!