If I just want types+js, Typescript is already pretty mature and widely supported (e.g. good integration with node, support for lots of popular libraries via DefinitelyTyped). What does this inferno offer over that?
According to the author of Inferno, TypeScript copies all the "bugs" and error-prone behaviors of JS, and is also a superset, not a subset. Inferno being a subset lets you use all your JS tooling directly with Inferno code.
Take a look at https://github.com/sinelaw/inferno It aims to add a type system to a subset of Javascript. It's not quite ready yet, but it already shows quite some promise.
There's also Flow and Google's Closure/et-al, but they are more lenient and accept more valid and invalid programs.