Flow doesn’t look particularly nice and like you, I’m not a big fan of transpilation in a consumable library. For finished products; a client’s web app for instance, there can be some savvy choices on transpiling vs minification vs modernising.
I’m excited by the working groups meetings on A potential Dict native, mixed with Symbol it could be incredibly expressionistic as a programming language.
Interfaces would be great to see before type safety though, I find it irrelevant to be type safe and transpile if the language beneath isn’t type safe. Apart from compile time warnings there’s no benefit.