When Swift first became available in the XCode 6 Beta, I rushed to write a simple app and use TestFlight to distribute it. Unfortunately, installation always failed. Troubleshooting showed that it failed via wired installation too.
I searched for a workaround to this problem, which I found today. Apparently, you need to manually package and use the `embed` and `sign` flags.
-sdk iphoneos PackageApplication \
-v “APP_NAME.app” \
-o “PATH/APP_NAME.ipa” \
–sign “SIGNING_IDENTITY” \