I suppose if it was easy and successful, nurseries might be selling minidwarf pears.
Looking at this post and followup, Aronia might be more challenging, due to scion overgrowing the rootstock? Im sure the different cultivars can have different effects. Also maybe letting some Aronia grow from the base, to support roots.
How about grafting apple Winter Banana onto Bud-9, and the desired pear cultivar onto that. Would the dwarfing effect be similar to that for apple? Or going cross species, and genus, not as compatible maybe so end result is smaller. Maybe.
I always wonder if the ultimate size of a grafted dwarf tree is similar to an ungrafted rootstock. In other words, if you grow out some M27 without grafting onto it, will that be a 5 foot tall bush? So a pear on a on Amelanchier that normally grows 5 feet tall might be about 5 feet tall, but one on an Amelanchier that normally grows 8 feet tall will be more like 8 feet tall?
I know the vigor of the scion cultivar has a role too. My Jonagold on M27 is about 9 feet tall. My Liberty on M27 is about 5 feet tall. Both are almost 20 years old. My Honeycrisp on M27 is only about 3 feet tall. Same rootstock, but big difference in size.