To give an example, Facebook Marketplace has become a considerable threat for "Small Items for Sale" category in emerging markets where classified websites other than Craigslist are dominant.

With its strong user profile integration that keeps out fake sellers, Marketplace has become a huge sell in countries like India, Pakistan and UAE.

I am definitely not surprised if Facebook would be going in for a vertical approach. Messenger used to be a part of Facebook. It's a stand alone product for a while now with bots for virtually anything (sellers are using them to give out promo codes), a separate mobile app and even a web app.

However, I don't see this verticalization to necessarily happen as a non-Facebook experience though. For Instagram, it makes sense to keep it that way and not bring it inside Facebook. For Marketplace and Events, it might not be the case because it needs that strong network affect and makes Facebook work as a platform to find, do and participate in things.