Precise error typing in Swift

If we need union types for error handling, could we introduce this as general-purpose support that supports any types? (e.g. support for any union types like Int | String, including T | Error)

The Commonly Rejected Changes list seems to mention union types:

  • Disjunctions (logical ORs) in type constraints: These include anonymous union-like types (e.g. (Int | String) for a type that can be inhabited by either an integer or a string). "[This type of constraint is] something that the type system cannot and should not support."

Type unions have always seemed like a broadly useful idea to me, and I'm not familiar with the background/context around prior discussions. T | Error seems like a natural and precedented spelling for a feature like this (that could be broadly useful outside of error handling).