My argument is that Swift will be primarily used to write high-level apps. For these apps, message passing is almost never a bottleneck. Swift is not going to replace the optimized C and C++ code, especially for the really low-level stuff.
But even if Apple does decide to rewrite all the Core* frameworks et. al. with Swift, there's still an argument that Swift should use message passing by default, and a way to opt in to vtable and direct dispatch for performance-critical code. For higher-level apps, message-passing is a lot less useful if it's opt-in.
As for the IRC and Latin conjugation, yes, those problems can be solved in other ways, but those other ways involve more (mostly glue) code. Trading more code for execution speed is the wrong tradeoff when performance is good enough.
You're correct I want to stick with Objective-C, but not that I have little experience with functional programming. I love functional programming. I love most of Swift. But for the specific problem domain of Mac and iOS apps, I love Objective-C. It makes working with GUIs much easier than anything else out there, and the ability to method swizzle Mac apps is great for third-party add ons.