The iPhone and iPad are fine platforms; I use them regularly for my work. However, they are a far cry from Alan Kay's Dynabook idea. A better base for developing on the Dynabook idea would be the Microsoft Surface line of tablets, which can run the full versions of Windows 10 Home or Pro and thus can run modern Smalltalk implementations such as Squeak or Pharo.
I wish there were more work done in the area of composable GUIs, where the core logic of applications is scriptable and where these elements can be combined in ways that could be even more expressive than Unix pipes are. Every now and then I have thoughts about taking a modern Smalltalk implementation and writing a suite of composable GUI apps as a demonstration of this idea.
This topic always takes me back to a Hacker News comment I read many years ago (https://news.ycombinator.com/item?id=13573373) about composable software versus monolithic applications and how commercial software companies are predisposed to support the latter while the free software movement should have focused on the former. I still don't think it's too late, however, as long as there are some vendors selling hardware that users can install their own software on without needing to use a certified app store.