I really don't like ads just like most everyone else, but I can't help but feel there is a missed opportunity here. Facebook just put classic mobile letterbox ads in a side scrolling container.

In such a unique platform such as Messenger you could get a bit more creative. One such example: Suggested pages to message. This would get companies leads and keep people on the Messenger platform. This might not be the best use, but with this product, Facebook can do better than just a re-skin of mobile banners.