This is not a valid comparison. As I’m sure you’re aware from the perennial “Array subscript should return optional?” pitches here, Array vends a trapping subscript because the performance penalty associated with having it return an optional would be unacceptable. This logic doesn’t apply to literals, where performance is an irrelevant concept, since (barring ICU dependencies, which don’t apply at the level we’re talking about) they are a purely compile-time construct.
There are tons of examples in the standard library of APIs which return optionals to the detriment of ergonomics, even when the optional case is a rare edge case. Unsafe${Mutable}BufferPointer.baseAddress comes to mind as an example. And I think a buffer pointer with a count of 0 is a far less common occurrence than a Unicode.Scalar outside of the ASCII range.