I have an idea for improving the compilation time. It’s based on Carthage. Basically instead of linking projects, we just provide a compiled version of the frameworks and only in case we change any source file from these frameworks we recompile them again (I think we can introduce this in the workflow with some scripting). If you think about your app features there are some of them that are not touched that often. For those one a compiled framework would work and help with the compilation time.
iOS 8 and dynamic linking affects very badly to the launch time. I don’t know improvements other than wait until these target of devices gets deprecated or just apply any of the tricks that the Artsy guys came up with. You can also use static libraries instead of the dynamic linking but then you’d be forced to use Objective-C.
Unless… Apple supports static linking for Swift which in that case, problem would be solved.