I see so many articles of people who have tried Swift Playgrounds app on iPad for development, that Apple announced in WWDC. But I am not able to find an ipa/download option from developer.apple.com. The public version is coming out in July, but I am not sure if a registered developer (with a developer account) can get access to it right now.
You need the iOS 10 Beta 1 (at least, if someone reads this in the future).
They have a "special" App Store in the betas, for the removable stock apps.