It is not a unique approach. We’ve been doing FAR MORE in Codename One since 2012 see: https://www.codenameone.com/
Pretty much every “wish list” flutter has already exists in Codename One and has existed for a while. We support more platforms, more tools and we’ll soon support Kotlin if you don’t like Java...
We already have 2 GUI builders, complex theming tools, simulator tools, CSS and integration with pretty much everything. We work on Linux, Windows and Mac while still working for every target possible.
We are open source and always have been.