What would change your mind regarding ruling out illegal structures?
In an alternative universe, there could be n sentinel non-values, instead of a single null.
There could be "null" ("I am initialising this memory as uninitialised"), but there could also be "egad" ("this pointer refers to memory on a different page"), there could be "biff" ("this address is on another caller's stack").
There are infinite ways you could design a language which lets you take invalid memory and tell the type system it's a Sheep, when it's not. Some of those languages might even have sophisticated biff-checkers or raise EgadReferenceExceptions.
What's stopping you from throwing out null along with biff and egad?
In an alternative universe, there could be n sentinel non-values, instead of a single null.
There could be "null" ("I am initialising this memory as uninitialised"), but there could also be "egad" ("this pointer refers to memory on a different page"), there could be "biff" ("this address is on another caller's stack").
There are infinite ways you could design a language which lets you take invalid memory and tell the type system it's a Sheep, when it's not. Some of those languages might even have sophisticated biff-checkers or raise EgadReferenceExceptions.
What's stopping you from throwing out null along with biff and egad?