The Halo5 Beta NEEDS to have Forge implemented for testing.
There's no "Ifs", "Ands", or "Buts" about it. Each time there was no beta for something, something was screwed up.
Halo2 had no beta and game breaking glitches were found from the start.
Halo3's Beta didn't include Forge and it turned out to be a pain to work with. Had it not been for the New Round glitch, Halo3's Forge would have been a nightmare.
Halo Reach...well, to be honest, I don't remember if it had a Beta or not. So please feel free to fill in this blank.
Halo4 never git a Beta at all and it was screwed up on all kinds of levels including Forge.

The Halo 5 Beta ABSOLUTELY, POSITIVELY NEEDS a Forge option.
I don't think any Forgers will care all that much if our creations don't transfer to the final game or not. So long as we get to test it out and report issues before the game goes Gold. This. Is. Needed.

I can tell you two things.
1) Players need to be able to forge inside terrain (as in Forge Island).
2) Forgers need to be able to remove/move/adjust ALL killzones from maps. Having usable terrain that is cut off from use is utterly stupid. Sorry but it is.

Here's a WILD Forge idea.
Why not allow us to move, and rotate terrain peices?
Give us a large and completely blank 'Forge Planet' canvas. Give use terrain peices to work with. They can be the most expensive items in the pallet. But allow us to recreate all of the maps from the past. If not all of them then some. But GIVE THE PLAYERS THE CONTROLS. By this I mean, if we want to move the Blood Gultch peices into the water, then let us Unlock it and move it. But also let us rotate, resize, and mirror it. Let us change the texture from Spring, to Summer, to Fall, and to Winter. Let us Duplicate that Blood Gultch piece and add it somewhere else incase we need extra land. Same for Plateaus, Caves, Islands, Cliffs, etc. Imagine a race map that sgarts off in a Winter Blood Gulch and takes you around a Dessert Island, up to a Summer Forest filled Plateau, and through a Spring filled Cave before returning to the start. Or imagine it also taking you through Pitfall and out into Terminal, before sending you to Installation 04, and teleporting you to Impact where a cave sends you to Valhalla, and so on. The possibilities would be endless!

Doing the above will come close to giving us Far Cry and Project Spark map creating abilities without actually doing it. This way it's easier to manage the credit system. Plus it'd be super cool.
Just an idea.