I'm currently playing the Horizons III modpack and it seems as though Itemducts from Thermal Dynamics aren't able to pull from the bottom of (quantum) backpacks. The pipe connects and I can put in a Servo, but it doesn't pull anything, no matter what the supply settings are for the backpack. Vanilla hoppers work.
Embers item pipes also aren't working with backpacks, and won't even connect to the backpack visually, although this could be Embers simply not counting it as a possible inventory.
It seems like the only option in the pack is just using vanilla hoppers, which is a bit unfortunate since they are a little bit slow, so I might have to have a big row of quantum backpacks all with hoppers feeding into some buffer chests that can be collected via itemducts, which seems inefficient to me.