I made combo apple-and-pear pies a couple of times. I don’t remember for certain why I stopped, but I seem to remember that the pears were hard to slice and once baked turned noticeably mushy.
Also there is such a thing as sweet potato pie. Apparently it is used as a substitute for pumpkin pie, or at least that was the way our grade school cafeteria used it. I’m assuming giant cans of sweet potatoes were cheaper than giant cans of pumpkin.