I tried to create some miniature pear trees by grafting onto serviceberry, aronia,and Chinese haw. The ones on seviceberrry and aronia both took but remained too tiny after two years so I threw them away, The one on Chinese haw is thriving, maybe too much for my miniaturizing ambition. Im not sure of the cultivar, the tree was here when I bought the property. I think it looks like Nijisseiki.
I cant remember for certain. I believe at the time I was looking at research reports regarding dwarfing pears on proprietary serviceberry rootstocks. Some cultivars works a lot better than others. I just used cultivars that I could find, so not a scientific test at all. Cottoneaster also works but again which cultivar. If Im not mistaken, Cottoneaster is highly dwarfing but you have to let some of the understock grow too or it wont survive.
I grafted Winter Banana onto an apple tree. Winecrisp, then grafted a Bartlet onto that. It survived a couple of years and made one small pear then was removed when I wanted to reshape the tree. The novelty had worn off by then.
On the other hand, I had a multigraft apple. Not sure of the interstem. The varieties were Rubinette, Queen Cox and Pristine, I added Dolgo crab, Goldrush, King David and Hawkeye. Everything took and survived, most thrived, then the Pristine branch just fell off at the graft union, Probably six years old, quite productive, maybe 8 feet tall. Semidwarf tree. There was one sliver of cambium connecting, the end survived long enough I took some to graft, parked it temporarily on Akane and now on Bud nine. Doing fine. No idea why that thriving graft failed.