Any time you support a variable number of args it is more complex! The implementation is about the same number of lines of code, but the tests need to grow a lot to achieve adequate coverage. It also means that if we do make `concat` or `interleave`, they will also need to support variable arity, which may or may not be easy to implement.

I don't see a huge advantage in usability when you can achieve the same effect using `_.reduce` like so:

```
_.reduce _.rest(streams), combine, _.first(streams)
```