The swift language is absolutely fantastic. But the constraints (such as objective-c compatibility) made it a juggernaut.

It's actually very surprising they managed to get that language work at all given the size of it. In that regard, i wouldn't say execution was bad. It was just unrealistic, and too much was asked from it.

ObjC interoperability is a solved problem now for Swift. They are even adding C++ and Java interop too!