Q: Where are Movie Trailors on ATV 4g?

Yes, it seems to have gone, at least for the time being.

If you have any suggestions that you think might enhance the Apple TV you can send Apple your feedback here

Other people outside of the US are also noticing this. I am in Canada, and there is no Apple Trailers app in the App Store, therefore it isn't available to be downloaded on the new Apple TV. This is unfortunate, since Trailers are available on the previous generation Apple TV, with information specific to the country. Hopefully Apple releases a Trailers app outside of the US soon.

If it's not a US only thing for the time being then you'll need to find it either within your purchases or search for the it manually in the app store.

I'm in the US and it wasn't a default app.  I had to go searching for it within the app store.

There's a Movie Trailers app, which you need to install. At least there is in the USA. I don't know if that app is available outside the USA.

What is the name of the app, perhaps I'm searching the wrong name.

It's not available in the UK App Store. Very disapointing.

I tried switching regions and it is clearly available as a download in the US store but definitely not in the UK yet, as the US store won't let you download in the UK.  Most frustrating as I used the trailers feature a lot on my v3. I am using the Plex app and that lets you access trailers through "channels" but it's not as good as the original Apple app!