I don't think Ripple's stablecoin will become the US CBDC because Ripple is not the FED. CBDC is money issued and managed by the central bank, not by private organizations like Ripple or Tether, so we can rest assured that Ripple will not create CBDC for adoption in the near future. Ripple's stablecoin will likely compete with USDT and USDC, although I'm not sure about this, we don't have much information to make a judgment.
However, I wouldn't be surprised if the future US CBDC is deployed on the Ripple network. Ripple's technology is really good, their partner network is very large and could become an environment for the FED to experiment or deploy CBDC. This is also just a possibility, the bigger and better possibility is that CBDC will be deployed on a public, decentralized and secure blockchain - Ethereum.
Of course not. But the FED can make a partnership with Ripple to make its own CBDC. Ripple can manage network operations (nodes, consensus, etc), while monetary policy will be in the hands of the FED. A much easier route would be to declare any of the popular USD-backed stablecoins as the official US Digital Dollar. It could be Ripple's new stablecoin, Tether's USDT, Circle's USDC, or even PayPal's PYUSD.
Given how popular crypto/Blockchain tech has become, I think this will happen a lot faster than we've previously imagined. I'm just speculating here. I don't think the FED will use a public blockchain network because that would reveal all of its activities on-chain (transparency). A privately-owned chain, or a chain with privacy features would be most suitable for the new CBDC. The future can't be predicted, so we can only hope for the best.