It probably works better to swap the types to MaybeUninit<UnsafeCell<T>>. Then the decision whether to get a mutable reference or not can be made later. This helps making a nicer abstraction for a consume operation, and the maybe_uninit feature wouldn't depend on nightly. Have to think it through a bit more.

Late night ideas don't always work 😄.
To initialize a MaybeUninit<UnsafeCell<T>> you either have to do:

• let slot = (&*self.value.as_ptr()).get() as *mut T;
  slot.write(value);

  which is UB, because it is creating a shared reference to an uninitialized type.

• let slot = self.value.as_mut_ptr();
  slot.write(UnsafeCell::new(value));

  which is not possible, because we don't have a mutable reference to the MaybeUninit.

The mention of UnsafeCell in the description of MaybeUninit::as_ptr threw me off.

Turns out we can't use MaybeUninit -- we'll need #[may_dangle] for dropcheck, and it only is avable in nightly.