After working in Project Spark for the last 2+ weeks, I can attest that this is a MUST HAVE. However, unlike Spark, we would need to be able to also streatch objects. Otherwise we'd be running into the same issue that Spark users are now. Still having to use multiple objects to get a simple shape we need. By simply asking for scalable objects, we're asking for a all dimensions to be locked to a aspect ratio. But allowing us to stretch and squish objects, it allows for far smaller forge pallets without loosing the amout of uses but increasing them.

It also needs to be noted that a object's textures need to be automatically locked to size with the object. Only after unlocking it should be be able to change the texture's size/tile, rotation, and location. Also something not possible in Project Spark.

The biggest issue with this feature are the items' hit boxes. Items like swords and other weapons that (with this feature) could be used for construction have very different hit boxes then other objects. I've experienced this more then once in Project Spark where a sword or shield was used as a platform or wall but it's invisible hitbox was twice as large. Which resulted in characters getting stuck in it during placement or seeming to hover high above the item.

Not saying it's not possible because it is. Just that there are certain factors that need to be thought of and included for this to work properly.

: Invisible Walls: cut off pieces of the map without blocking scenery. Glass
: Mazes!

This is already possible (sorta). In any CTF gametype, if you set any item (except flag stands) as Neutral and then as a "Flag Return", that item becomes invisible. Vehicals and players can not pass through them but grenades and bullets can. The new Race gametype has a similar feature where you simply set it as "race hide". No reason this couldn't be added to all gametypes.

By the way, I did a invisible maze recently. Tough it makes for a cool and sometimes funny map, in the end it only frustrated players. Mostly because it was so difficult to reach their goal even though they could easily see it, but also because it caused too many players to get both trapped, and continue to run forward thinking the way was clear but going nowhere because of the "glass" wall. Other times, plYers would shoot or melee the others through the walls. Oh yeah. This also works with vehicles.

: Custom Image Previews for maps in lobby/website.
: All Forge-specific spaces MUST come shipped with the game on disc - no more
: late releases a la Foundry/Sandbox and Forge Island.
: No in-built invisible walls: Expect people to build outside the usual bounds
: and let whatever will be, to be.

Yes and Yes PLEASE!

: Importer for Halo 3/Reach/4 Forge Maps: Imagine 7 years worth of community
: content available on day 1 - WOW! Also, familiar Forge spaces would allow
: Forgers to hit the ground running with ideas for maps with new gametypes
: and maps enabled by new features.

Outside of the Forge specs so vets can "hit the ground running", this idea is not possible. Sorry. The different Halo Forge Modes are all too different from one another to be brought into one. Except possibly with Reach and 4. Also for it to work, all maps from those games would have to be included with their same graphics and physics and codes. It's simply not possible. If you want to forge on those maps, I'm sad to say that you must boot up those games.

: Proper in-game Forge Tutorial. Forge is still super intimidating to a lot of
: people. So I think a mode where 343 Guilty Spark actually walked you
: through the basic controls and object manipulation and guided players
: through making some toy map concepts would help a lot.

YES!!! YES!!! A THOUSAND AND ONE TIMES YES!!!!!!
Though it's pretty simple to build items and maps, it's the setting up of gametypes and settings that intimidates gamers. Seemed to take me forever to learn how to set up Invasion. Same with Extraction and Dominion. I still don't know what to do with the data numbers and what they are for. And I've been forging since Halo3!

: Virtual Reality object editing. Let me get my hands on those forge pieces
: and move them around naturally! (also need: Xbox compatible VR headset and
: neo-VR gloves)

This more falls in line with the use of the Kinect. It works very well on Xbox One, but I don't see it happening anytime soon. Not even if it was on the PS4 and used their wands.

: But by far my biggest wish is that just as much effort is put into the
: gametype engine and customisation thereof. As we saw in Halo 4 compared to
: Reach, maps are cool and all but changing the rules of play is (more than)
: half the experience.

Also YES!!!