Venmo / ZuckBucks / Paypal / Patron all are much simpler and more efficent for payments. Plus you don't have to buy the cryptocoins from someone who generated nearly for free and then and then jacked up the price, with Venmo etc it's instant and hassle free.
It never ceases to amaze me to see Bitcoin / Ethereum users try to come up with what-if services in an effort to trick others into thinking the database token is worth anything to other people.
How much would you bet against Facebook attempting to link Bitcoin/BitcoinCash/Etherium wallet addresses to individuals and tracking cryptocurrency transactions as part of your marketing profile?
Eagerly awaiting reports of individually targeted Facebook ads along the lines of "3 of your friends bought items from these Benzo and Ketamine dealers on the dark web! Use coupon code #HeyNSA! for a 25% discount on your next order over $250 at their SilkRoad or Agora stores!"
- allow Facebook users to pay each other using BitCoin & Co.(certainly the key feature as Messenger killer and under-utilised feature is its payment option, and Markus’ past at PayPal)
- allow Ethereum & Co. to leverage Facebook Identity (for instance, define “someone” as an active Facebook account with at least 50 active friends, the way I believe Tinder does) for their contracts;
- find a way to run a Facebook-compatible version of Mastodon/Diaspora/etc. off Smart contracts, allowing privacy-conscious individuals to host their social media-like experience on a platform compatible with Facebook but without a identifiable central repository or hard to maintain decentralised structure.
Only the last one is something that would make Marcus excited enough to leave Messenger. The first one is a Hackathon idea, the second probably a project that makes sense once Ethereum (for all its merits) has more compelling use case than a cat-collectibles to its name.