Not really since you are unlikely to end up with unpaired surrogates outside of UTF-16 unless you explicitly implement a WTF-16 decoder - most other things are going to error out or remove/replace the garbage data when converting to another encoding.

And if you convert valid UTF-16 by interpreting them as UCS-2 and then not check for invalid code points you are going to end up with either valid UTF-8 or something that isn't even valid WTF-8 since that encoding disallows paired surrogates to be encoded individually.

WTF-16 is something that occurs naturally. WTF-8 isn't.