Don't most swift apps also still drop to Obj-C? That will make them less portable.
Tim Cook said they would be open sourcing the standard libraries.
I'm assuming he's not talking about the GUI libraries, which would make it considerably less interesting. As far as I know C/C++ is still the only (free) way to write cross-platform mobile apps. If I can compile my apps on iOS and have them run on Android, then I am definitely interested.