Personal opinion, but I somewhat strongly disagree here. Even if those cases are common, it feels really weird to privilege them in the parser, when there’s lots of other domains and use cases where people want to talk about other types of unions, and the conflict between Missing and Nothing isn’t likely to be resolved anyways.
This one seems really unlikely to me. The ternary operator a ? b : c is already such a big source of confusion and parser quirks, and this would make it even worse. E.g.
a?
b : c
would mean something completely different from
a ?
b : c
if that operator was added.