So we can push even more features into 5 right? However I think we need some clarifications why the release is deferred? Is work around ABI taking again longer then expected?
One reason according to the SOTU is that one would like to get feedback for the changes done in Swift 4.2 in preparation for ABI stability which will be released at fall. Thus a few months of gathering feedback and a few again to discuss and fix the last issues naturally leads to an "Early 2019" release of 5.0.
That’s not a bad idea. I’ve actually thought once or twice that they ought to declare ABI stability in Swift 5.1 so they have time for last-minute corrections. Shipping 4.2 instead of 5 in the fall serves a similar function.