I would like to play devil's advocate
From this article I read
Unlike the volatility seen around other cryptocurrencys in the past, we believe that Libras focus on creating a stable, low inflation currency backed by a reserve or real assets is a differentiator. Further, unlike other stablecoins, Libra will not be pegged to one currency but instead a basket of assets ranging from bank deposits to short-term government securities.
https://www.cnbc.com/2019/06/18/the-difference-between-bitcoin-and-facebooks-libra.htmlWill Libra Coin bring Down Bitcoin's dominance in the market, your thought?
This is not possible, Libra isn't much accepte yet. In USA already 9-14 percent people have idea about Libra coin. European some country doesn't support Libra coin especially French. Could be down dominance of Bitcoin, when Ethereum 2.0 will arrive and Libra coin will launch.