It would feature on Binance first, then Kraken and other exchanges.
Coinbase would likely be the last to list it because it partly owns Circle, which manages USD Coin (USDC).
RLUSD represents competition for the USDT-USDC duopoly at present (which is, to be honest, mostly a USDT monopoly).
The only way I'd see Coinbase listing it sooner than later is if it buys a portion of Ripple when it goes public; it is expected to IPO later this year.
There's also the rise of synthetic assets such as Ethena's USDe (USDE), which is currently in third* spot behind the USDT and USDC.
* If USDE were to be categorised as a stablecoin. Strictly speaking, it's a synthetic asset, not a stablecoin, but is often placed in the same category for comparison.