Idea / Pre-RFC: Null-free pointer and Zeroable reference

Fair, I withdraw the UB concern here; the remaining concerns still stand.

CodesInChaos:

Cell and MaybeUninit don't have field projection support either, and those are much more common.

Cell exists to hide references behind interior mutability; MaybeUninit exists to hide uninitialised memory. Field projection is a nice-to-have feature, or even a soundness hazard for them - their purpose is fulfilled without field projection or aided by its absence. A zeroable reference is the opposite - transparent access to fields is its entire purpose. Without field projection, it doesn't become verbose; it fails to be what it is.

And looking at replace_memory in your any_mem sketch, that's the operation ptr::replace couldn't do soundly because it relies on &mut *dst internally (rust#138351). Your playground itself annotates read_memory/write_memory as "needs compiler magic" - doesn't that confirm the gap has to be closed below the library level?