Maybe with an alternate or additional link so you can choose whether or not it will pull from a cart, maybe it just does it

Maybe even make it so if a chest minecart is linked to a hopper minecart that is linked to a furnace minecart, it just pulls from it. Though if hopper minecarts have a ui, would be easier to just use that directly

Hopper minecarts could work too.

I think this could be part of an interesting mechanic without changing how hopper carts currently work. Add a sideways hopper cart that just tries to move items between carts. That would allow much more interesting cart loading and unloading, bigger refill trains, and of course refueling of furnace carts.