I work for some bigger company as javascript developer. We have about 30 web projects. But we don't use any MV* for javascript.
1) I think that it doesn't worth till you have only few javascript developers. It is better to have set of widgets and reuse widgets from this set. Each widget is an object in our case. Javascript is mainly view so why to separate it into more parts?
2) The main downside is that you are trying to use too big hammer, so it extends development time. Filtering, searching, sorting, ajax and other stuff are very common and simple problems. You don't need MV* patterns for these.
3) Supranational organizations can afford it. Also you can find it in some webGL projects (games) and similar things. Others don't need it.
Also don't forget that "premature optimization is the root of all evil". Good frameworks and clear code can help you in the future, but it can also stop you in the present!