I believe in the not too distant future, we will get an app, it could be an updated Swift Playgrounds or a completely new app. For now I believe no matter the origin it will be marketed as something new, something like “SwiftCode”.
Swift came out several years ago, and it's been slowly building into a stable platform for apps. Little did we know, it would be the platform for the future of Apple development. SwiftUI was released this year at WWDC which is entirely new paradigm for developing apps. Why would Apple build Xcode for UIKit, when they have known for years that it's not the future of their platforms? Instead I believe SwiftUI is the beginning of an important transition. One step of that will be a completely new IDE that will sometime in the future (read 10-20 years) completely replace Xcode in the Apple ecosystem.
SwiftCode will be built using Swift and SwiftUI to the core, built for a cross platform experience of development and it will let go of all the old ways of programming. Brent Simmons wrote a great piece talking about the difference between the NeXT Era and the Swift Era, I completely agree. This new development tool when released will live alongside Xcode for awhile allowing people who are all in on the Swift era to develop on any platform they wish, and Xcode will continue to exist for the foreseeable future for backwards compatibility of old development workflows. It'll take awhile before everything can use SwiftUI and the new Apple development tool chain, but I believe an app like SwiftCode built to run on iPad and Mac, and who knows, maybe even iPhone, will be the future of Apple development.
That is why Xcode for iPad hasn't and never will be released. They had to finish the foundations first, the Swift toolchain, Swift Package Manager, and SwiftUI. All the pieces in place so that they can release an IDE custom built for that ecosystem: SwiftCode.