The issue for me is four-fold: 1. Adds complexity to the language 2. Adds complexity to engines 3. Adds complexity to developers, especially new developers (

The issue for me is four-fold: 1. Adds complexity to the language 2. Adds complexity to engines 3. Adds complexity to developers, especially new developers ("wait is it typed or not") 4. Most importantly, all but guaranties we will never have true types in JavaScript for things that could benefit from it like node or electron where instant compile time isn't necessary. All this for a feature only helping some developers some of the time so they can run code that will be stripped out in production to reduce size anyway on their local browser a bit more easily.