It’s related to another idea that I had: TypeExpr-specific constructors. See this post.
I personally suffered a bit from the infectious nature of using string literals for forward reference:
T = "AvailableLater" | AvailableNow
# TypeError: unsupported operand type(s) for |: 'str' and 'type'
That’s where I think DeferExpr will come handy.
BTW I cannot recall any prior discussion on typing in this thread.