It sounds more like "path" borrowing than "group" borrowing to me, but the idea is great! Quite eye opening!
One minor thing is that I'm not sure why they had to have "in" keyword for sub-borrows. Wouldn't it be more consistent to see "entity &world.entities[?]" instead of "entity in world.entities[]"? We'd consistently get the borrow "&" symbol and open the door for some contracts on what index (range) is affected.
One minor thing is that I'm not sure why they had to have "in" keyword for sub-borrows. Wouldn't it be more consistent to see "entity &world.entities[?]" instead of "entity in world.entities[]"? We'd consistently get the borrow "&" symbol and open the door for some contracts on what index (range) is affected.