I dont think that Libra will domninate the bitcoin market as it is meant to be a stable coin. Stable coin and crypto movement does not go well to make it bigger in the market.
like trading with a USDT pair I think libra can take an important role in the market. It does not dominate the bitcoin market trading but it would be better to trade with altcoin or other assets. except libra is only made for their community. then it will not affect the bitcoin market at all.