In fact GG simplicity and usage has lot of similar points to Far Cry 4 editor lol
GG only needs some lighting and workflow improvments (FBX import, easy to make any custom npc, easy entity system and editing , prefabs) to become more modern.
Some feature i would surely vote would be GG becoming an open world game engine in the long term.
It could be achieved using terrain tiles with occlusion, and only displaying tiles around player with objects on top of these terrain tiles, npc groups load/unload based on player distance for example.
What i like about the Far Cry 4 editor is the optionnal top bar showing the RAM , objects and performance around the zone you are editing in real time