Previous discussion: https://news.ycombinator.com/item?id=31663298 - it's downright mindblowing that all this seems to be the work of primarily a single developer.
For a less intrusive solution, https://github.com/jquense/yup is a great library to reach for whenever you're defining the shape of a network-transmitted object and don't want to introduce compilation stages.
[0] https://github.com/arcanis/typanion
A definite high point of my time with it was when a requirement came along to allow users to resume signup - because all the form state was in the Redux store already, it was simply a case of serializing that and putting it in localStorage (or wherever), then reloading it as the initialState.
There are performance issues to be aware of if your form gets too large, caused by the "top down re-render" effect of having the top level ReduxForm HOC connected to the form state and therefore re-rendering on every keystroke - often these can be solved by splitting the form into sub-components with appropriate shouldComponentUpdate etc., but this isn't a perfect solution - see https://github.com/erikras/redux-form/issues/123 for a lot of discussion. The new v6 API aims to solve this, by removing the need for a single top level component: https://github.com/erikras/redux-form/tree/v6
I've been intending to write up my experiences and how I've been working with it, but decided to hold off until the v6 API stabilised, so that I wasn't giving outdated advice. Happy to answer any questions in the meantime!