一旦履歴を辿ってみたところ、 ImplicitlyCopyableConsumingはかつてTransferringと呼ばれており、sending用のcaseみたいですね... consumingは暗黙的にno implicit copyableで、implicit copyableなconsuming ということをsending用に表したもののようです。

I cannot use consuming for this purpose since consuming today implies no implicit copy semantics, which we do not want unless the user specifically asks for it by writing consuming.

https://github.com/swiftlang/swift/pull/71567/commits/1f0527d47f347a9737f37592f99e15832b034f8a isNoEscapeに関しては 1. We don't support no escaping closure parameters today and would like to leave the design space open. という理由からでした。 https://github.com/swiftlang/swift/commit/4d7af7be25d99f453a732c4ed732edf64bdf137a (edited)