I would like to use the Xcode 9 beta for use in development but I can't seem to get the correct settings for using Swift 3.2 within Xcode 9. The editor is much quicker than Xcode 8.3.2

I can (and have) downloaded the Swift 4 toolchain from swift.org and can use it from within both Xcode 8.3 and the Xcode 9 beta. If I wanted to ship my app before Xcode 9 is officially released, could I write it in Swift 4 and then submit it to the App Store via Xcode 8.3 using the Swift 4 toolchain?