Navigation Architecture Component - Activities

I've been following the docs from Navigation Architecture Component to understand how this new navigation system works.

To go/back from one screen to another you need a component which implements NavHost interface.

The NavHost is an empty view whereupon destinations are swapped in and out as a user navigates through your app.

But, it seems that currently only Fragments implement NavHost

The Navigation Architecture Component’s default NavHost implementation is NavHostFragment.

So, my questions are:

Even if I have a very simple screen which can be implemented with an Activity, in order to work with this new navigation system, a Fragment needs to be hosted containing the actual view?
Will Activity implement NavHost interface in a near future?

--UPDATED--

Based on ianhanniballake's answer, I understand that every activity contains its own navigation graph. But if I want to go from one activity to another using the nav component (replacing "old" startActivity call), I can use activity destinations. What is activity destinations is not clear to me because the docs for migration don't go into any detail:

Separate Activities can then be linked by adding activity destinations to the navigation graph, replacing existing usages of startActivity() throughout the code base.

Is there any benefit on using ActivityNavigator instead of startActivity?
What is the proper way to go from activities when using the nav component?

Solution

I managed to navigate from one activity to another without hosting a Fragment by using ActivityNavigator.

ActivityNavigator(this)
                    .createDestination()
                    .setIntent(Intent(this, SecondActivity::class.java))
                    .navigate(null, null)