A thought—
Today, it is possible to test IntegerLiteralType.self == Int.self (for example); not sure if it's the best solution for anything, but it is possible to do and works as expected.
I would imagine that someone, somewhere, will want to write DefaultActorIsolationType.self == MainActor.self. Can it work as expected (even if it's not the best solution for anything)?
A tangentially related thought—
Should we infer the typealias to be MainActor for top-level and/or playground code so that our documentation examples work again without caveats that upend progressive disclosure?