Comment by rishflab

physics is not easy. its pretty challenging and has unending scope.

audio can also have unending scope if you want to do physically simulated Spatial Audio.

Im not sure if AI/pathfinding are worth developing as part of an engine. I feel like their implementation is heavily dependant on the game type, engine implementations often get in the way, rather than helping.

rendering is a beast, especially if you need a long draw distance and have a world that doesnt fit into gpu memory.

The whole task of putting all the pieces together into a cohesive package is a huge undertaking as well.