(also, I disagree that for DST-aware `MaybeOwned` that `~[T]` and `~str` are not so useful anymore.  I think the `MaybeOwned` example serves as an example of where you *do* still find utility in `~[T]` (and `~str`).  I do not know if it is clear, but to me, the point of the owned cases in `MaybeOwned` is not that the caller will want to own/modify the data itself: It is just the callee passing back the obligtation to drop the owned object back onto the caller.  It is not meant to offer any utility beyond what the `&T` variant of the enum offers; just the obligation to drop.