Qt does not (and cannot) support Windows "Metro." By the same token it won't be able to support this new environment
Nah, this isn't something like metro. Swift is just another language, not a new runtime.
Swift actually has good interoperability with C and ObjC. You can link precompiled libraries or just drop C code into your project, #import the header files, and call C functions directly from swift or vice-versa.
Alas, it doesn't have the same interoperability with C++. Apple recommends creating a C or ObjC wrapper for C++ libraries, which doesn't sound awesome.
However, QT already links with cocoa, apple's ObjC / Swift interface. Cocoa isn't going anywhere, so QT won't be going anywhere.