I'm guessing the reason is more involved than "because nobody asked", but such a capability would be nice for my dinky little LazyObject class. I suppose a reasonable workaround would be to force my SmallInteger into a Large(Positive|Negative)Integer, or make a wrapper for the SmallInteger.
"All I need to know about Smalltalk I learned from Sesame Street" magicianMumford become: PeanutButterSandwich new.