As someone who makes twist chew a lot - this is very valuable - thanks for sharing.
I'm not sure that machine is for crushing the mid-rib as much as it's for flattening out the leaves ... as you can see from the video at 40-43s the leaf they are adding to the twist is in halves with the mid-rib cut out.
A key thing to take away is just how high a case these leaves are in when they are being twisted - presumably with the prepared casing liquid containing the sweet liquorice taste all the oliver twists have. Putting the leaf under shear forces like this does, it can easily tear if the case is too high, and if the tobacco is in too low a case it risks becoming brittle and making the rope raggedy.