Okay, it works. I have tweaked the synthesis of the coroutines so it yields the wrappedValue in case we have a property wrapper and the code now runs as fast as it did without using a wrapper.
I also had to change the property's ReadWriteImplKind to Modify. Does this approach look okay @John_McCall?
(oops, just realised I posted in the wrong thread, I should've posted here. Sorry)