By my reading the author made that statement, not naively, but with full awareness of it's slightly ridiculous nature. I think that whooshing sound was their joke going right over your head.

Author here. To be fully honest, it's somewhere between the two. Yes, I'm aware of the irony of the statement. But what I failed to make clear in the post is that the code in the last two examples passes the type checker. Where it fails is at the intermediate representation stage. So the grammar of the language supports the constructs but the backend hasn't caught up yet.

It's possible, of course, that Apple will modify the grammar to make these use cases impossible. But I would be very surprised. I can't blame anyone for accusing me of rose-tinted glasses until we know for sure, though.

An early beta compiler crashes! Oh, noes, Apple is doomed!

I think the point here is that if the compiler crashes, that implies that it is trying to do the thing, as opposed to saying "No, filthy programmer, I will not permit you to do that thing."