[the_why_of_y]

> Perhaps every pointer could be implemented not only as a raw pointer but one with a "valid" range attached

The main problem with this is that it's incompatible with every existing system C ABI.

There's also the problem of real-world C code converting pointers to integers and back again, but the compiler could define uintptr_t and intptr_t accordingly and code that uses other integer types is broken anyway.

> it is possible to create a new kind of "top-level context"

I'm not familiar with that, it sounds like quite some effort but I'll grant you that likely it can achieve what you claim.