I think in Halo 5 forge should include forerunner, covenant and UNSC pallets. Also there should be more forge maps and to have a map what is within a human colony, an example is the map landfull in the majestic map pack.
Also they should include weathering and night and day control, futhermore it will be good if you would be able to make a firefight map on forge if firefight could come back.
Furthermore weapons, there was'nt alot of crazy inventive weapons in Halo 4 such as the needler was a creative weapon through out Halo. Vehicles there wasnt alot of them in Halo 4, that the banshee was the only flying vehicle and there wasnt any promethien vehicles.