Libra will be substantial, everyone concerned with Governments, when Venezuala launched their Petro Dollar Coin, OPEC told everyone not to Buy it , and that basically meant it was not going to be accepted anywhere else for Oil ever, and it killed the Petro Dollar. This happened because Maduro is a Dictator oppressing his people, lowering their currency to less than the face value of Toilet paper, so it is better to wipe with Venezualan Pesos after using the bathroom, because of Maduro. The Venezualan people are safer using Crypto than their own Pesos.
Facebook is a different Story.
Facebook already has Games, Donation features, and multiple Platforms (Facebook, Instagram, WhatsApp) to add Tip Widgets to. So Libra has utility right when it launches.
Plus it is Proof of Stake, so not just a reason to Buy it and spend it, but Buy and Hold it.
Then I assume Libra will have a VM or something like Graphene or the Ethereum EVM, so there will likely be Libra dApps and Tokens, and many of those FB App making companies have much larger budgets and user bases than most ETH Devs, so if Libra is a IaaS/PaaS Blockchain, it will have a jump start over existing chains.
Having a Game and maybe a Libra Token Smart Contract running your game, it is easier to access than Meta Mask, etc. Everyone is already on Facebook and they have lots of in App Purchases for FB games.
So that right there Fuels the Market, and the people collecting fees for Developing those Smart Contracts have incentive to hold because it is PoS.
And we could even see a Cryptocurrency exchange, or many, on Facebook.