There will be a huge hype wave with Libra launch and a lot of people would invest in this coin, but how should it stop the increase of BTCs dominance? As far as I understood, Libra is nothing else than a stable asset.
With many conspiracy and many bad news about this project chances to have more hype after releasing it to the public is very possible. That delayed launch and more news that includes this project bring more interest for spectators who loves to play inside the market. But even with those millions of social media followers Libra project will be centralized and controlled while bitcoin will continue to dominate as a decentralized chain which most of the investors will keep for the reason of being anonymous around.