C and C++ could have non_nullable pointers, easily

True indeed. However, for nearly all programs (i.e., everything other than
kernels and those very rare userspace programs that dereference things at
address zero or have structures whose sizeof() is in the multimegabyte
range), dereferencing null pointers doesn't lead to a root hole, but to a
crash. DoSes are bad enough, and it's still a bug...

So, yes, it's an improvement, but I'm not sure it's a large one. (I also
fear it would turn out like 'const' too often does: the semiclued majority
would just use nullable pointers everywhere because non-nullable ones
are 'too annoying'. But security-important software and software written
by clued people which can't use real languages like ocaml ;) would of
course benefit. And perhaps that's all we can hope for.)