Also a -1 (for different reasons than above).
I don't think this feature has gone through anywhere near the required level of prototyping or field-testing for a language that claims 'world domination' as a goal. This speaks to a larger problem with swift-evolution rather than this proposal specifically.
If you read the pitch thread, you'll see that the proposed syntax changed pretty wildly - for one thing there used to be a requirement that property delegates be implemented by a type with a single generic parameter. That seems to have been a requirement less than a month ago. If you went on holiday or had a busy week or two, you could come back and find something totally different to when you left.
Swift needs an "experimental" mode where we can test these kinds of features, and those features need a long-enough incubation period that we can find the difficult edge-cases. It is absolutely bonkers that the server work-group has a more thorough evolution process than the language which it targets.
When such big features can go from pitch to radical changes to proposal in less than a month, it makes Swift seem like some kind of mickey-mouse language. The first pitch thread is literally 25 days old.