Applications have been using out-of-process sandboxes for years. But that's not necessarily a sign of quality, since this comes with a performance cost.

It's nice when extensions don't crash the host application, but the mitigations aren't free. It's interesting that Swift's stable ABI will drastically lower that cost, since you usually need some kind of serialization (although people have been using mmap to share data between host/extension process for awhile too to avoid the serialization penalty)