for unit testing, the "virtual dom" or whatever you want to call it could be the key to success

It's certainly in the plan to be able to interrogate a composed tree for testing, the types of questions you can ask it are what I'd like to be careful with to avoid brittle tests. If you're testing a NewsStoryCard that includes a HeadlineSnippet with two bits of text, it doesn't matter if HeadlineSnippet changes its implementation from two Text elements in a Column to a single Text element with a newline, for example. That sort of change ideally wouldn't break HeadlineCard tests.

yeap, you'd need testing tooling around to be able to just ask for part of the implementation as Enzyme does for React

yeah, which gets a lot more interesting as you start flattening that tree, or start from a pretty flat tree to begin with