On a related note, I’ll add to all these useful thoughts that the reason we don’t consider using Swift in any of our core Comp Sci courses at Macalester is the poor state of support on all platforms that aren’t Apple’s.
Half our students have Windows laptops, and maybe 5% have Linux. Incoming students who are new to programming (and perhaps even a bit shaky with using a laptop at all and not a phone!) need to be able to do a foolproof installation from simple directions over a possibly mediocre internet connection and have a working environment on the first day of class. This is just barely even the case on macOS, but on Windows….
(More details on the non-viability of Swift for college teaching in this older post.)
I’m talking about students here, but I imagine the same barriers to adoption exist for many dev teams. This multi-platform story is in my view the main obstacle to @Chris_Lattner3’s dreams of Swift taking over the world.