This will be live by the end of 2019 in a similar form.
The MakerDAO stablecoin system on the Ethereum blockchain produces the DAI stablecoin, with 1 DAI pegged at 1 USD. There's currently $85M of DAI in circulation.
Each $1 of DAI is backed with $1.50 of Ether, the currency of the Ethereum blockchain.
Later this year a major upgrade will go live named "MakerDAO multi-collateral DAI". The "multi-collateral" bit is related to a basket of currencies.
By Q1 2020, the DAI stablecoin will be backed still by ETH, but also backed by USDC (a US dollar stablecoin run by Coinbase), REP (a token for the Augur decentralized prediction market), and other tokens.
Not exactly "a digital currency backed by a floating basket of currencies" but a related concept and in production very soon :-)
https://mkr.tools https://vote.makerdao.com https://makerdao.com
That said I have high respect for the Maker team and the overall idea. They are some of the best people working in crypto right now.
Let's not pretend any of the processors are doing this because they have ethical issues with Facebook. They are likely doing it at the behest of the Fed, the Treasury and other international currencies. It's about power.
Facebook would not have unilateral control by any stretch of the imagination.
Libra Association is the organization these companies have withdrawn from.
At minimum they are the registered owner the Libra federal trademarks...that's a funny first step for a "decentralized" project. Satoshi Nakamoto never trademarked bitcoin or blockchain for that matter.
I think what it'll take is a company with a profit (i.e. subscription/fee) model that clearly doesn't rely on pimping out consumer data to any/all comers and takes GDPR privacy to heart.