Allowing type checking on js files with comments will allow me to start improving our exciting hard to maintain large code base. I attempted to do this with flow as well before, and it did the job well enough (although at the beginning I ran into a number of issues), but I have a preference for TypeScript, and the next time I work on that project I will likely be doing heavy usage of this.
Please let us know if you see any errors while trying out new TypeScript 2.3 features in VSCode or have any thoughts on how our JS/TS support could be improved: https://github.com/Microsoft/vscode/issues/new
In my experience, in some organisations, it's hard to introduce TypeScript instead of JavaScript, because of reasons. For example, one of my clients made a bet on CoffeeScript back in the days, and that didn't work out, so now they are hesitant to adopt anything. Being able to introduce at least the type checking feature will start to drive change to this hesitation.