I love languages, and I want to use languages with powerful, sound type systems on the web, but I don't want to do it at the cost of shipping much larger amounts of code, making for a slow initial render.

A vanilla JS todomvc app is 10KB of JS (plus some analytics code for some reason): http://todomvc.com/examples/vanilla-es6/

The production build of the ReasonML todomvc app ships 5x as much, 56KB JS.

How much of that is a static runtime cost, and how much is just the cost of translating ReasonML into the corresponding JS? An extra 40KB isn't great, but it's not a dealbreaker. A shipping 4x-5x as much JS would be, in a lot of cases.