I have an idea for a mod, unfortunately I don't code. I'd like to see a mod with no "up" or "down, ala MC Escher. Anyone up to the task? I don't see a need for new weapons or graphics, just a way to change which way you fall. I'd suggest creating an entity called "trigger_down"... but then again I know nothing about coding.
Let me know if it can be done and I'll start mapping!