Would you add an option to add module slots to stacking beltboxes?
I like to use efficiency modules and it's pretty strange that due to lack of module slots beltboxes are second on my pollution producers list (after minning drills which I have about 5 times more).

In the very earliest version there was some GUI problem with it, I don't remember what, it likely doesn't apply any more.

I think in the past the electric cost and pollution were the non-negotiable penalty for making yellow belts effectively superior to blue belts. Efficiency modules are viable but speed and production are obviously a no-go.

This would be an option in the Experimental add-on if at all, I reckon.