As you seem to know something about this, what's an apple/pear hybrid like? I assume they do hybridise. How about pear/quince? That should be an interesting one.
An interesting hybrid though is x Sorbopyrus, a cross between a pear and sorb tree.
Can't cross with an apple but can with a whitebeam, I wouldn't have believed it. Amazing, thanks.
I'm guessing the Sorbopyrus you are describing is the Shipova: https://en.wikipedia.org/wiki/Shipova. It's a surprisingly old hybrid. I've got one growing, but haven't gotten any fruit yet. Have you eaten it?
You also need to plant pears in pairs in order for them to pollinate each other. There are tables with which varieties go well with each other.
Pears are not the easiest fruit to culture and in some areas is a doomed project from the start. --Don't-- buy trees in the supermarket without a sanitary tag. Go to a professional. Fireblight is a real pain
https://cornusmas.eu/catalogue/intergeneric-hybrids
has some information about some interesting mixes (and he sends out great plants if you are in Europe).
Palms also form fascinating hybrids and there is an active community of people around the world doing this and sharing information.
Pear and quince can hybridize producing a fruit called Pyronia (= Pyrus x Cydonia). Is not better than any of the parents, so it remains basically unknown and unavailable.