Transmute to user-defined types with all public fields?

That is the simplified version and what is already being done with macros in certain crates: you can transmute into types where all bit patterns are valid. But what is being researched here seems to be more general, e.g. you would in theory be able to transmute [NonZeroU8; 4] into NonZeroU32, though not vice versa, despite neither type having all bit patterns valid.