Consider adding an option for the opposite of culling (Optifine Smart Leaves)

[Madis0]

I suggest also considering an option that would render the "inner" leaves as fast leaves instead of leaving a "hole" behind. If fast leaves are complicated, maybe render a solid leaf color instead. That could have the benefit of rendering even less blocks, because some would be solid, therefore any blocks behind them would not need to be rendered from the player's point of view.

[luni3359]

What does fast leaves mean?

[Madis0]

What does fast leaves mean?

In video settings, set graphics to fast and you'll see opaque leaves.

[ghost]

You can use CullLessLeaves.