> Why should it not, one of the design goals of Swift as C, Objective-C and C++ replacement was painless interop with those languages.
This is actually a very good quality. I'm exploiting that for all it's worth in a job project where I'm gradually (file by file) converting a legacy codebase from Objective-C to Swift.
Providing an exit-strategy for Objective-C is good enough reason for me to at least have a basic working knowledge of the language.
Thus it is more an issue of Swift embedded toolchain being able to be used alongside FreeRTOS on the specific hardware target.