We already have the port built in this repository: GitHub - return/swift-haiku-build: Google Summer of Code repository for building Swift 4, 5 and higher for Haiku. and it is currently on Swift 5.9 so we are certainly not stuck on the older versions of Swift.
As for Swift for Haiku, I would not expect a full migration of another language (Swift, Rust) being introduced to replace another (C/C++) in the kernel or in the whole OS. Even if that was to be considered, it would ultimately be up to the core Haiku developers to decide on this.
But I personally would not want to mix two or more languages directly in Haiku’s kernel since it just creates more complexity and context switching into the project and I’d rather just keep it as an external third-party supported language in HaikuPorts.
Overall, I think Swift will benefit from the direct C++ interoperability feature to be used from existing C++ libraries and up to large-scale software such as browsers like Ladybird and already in Arc Browser (which uses Chromium as its core which is in C++).
But we’ll see how it goes over time, but any decision on any new language integration into Haiku has to go through the core team members.