Developer shares his findings on Swift Playgrounds 4 as primary development tool. Overall, developer was able to create and distribute app using Swift Playgrounds, although some limitations are quite significant.
App Store: ToDon't
Blog post: Lessons from Developing an App on the iPad in Swift Playgrounds from Start to Finish (Including Publishing on the App Store)
Reference: This to-do list app is the first created and published with Swift Playgrounds 4 on iPad