Tokens supported by Payment Abstraction are allowlisted for both security purposes (e.g., to block malicious tokens) and to ensure there is sufficient onchain liquidity for conversion into LINK. The first alternative asset supported is ETH (and its ERC20 wrapped version WETH), which has predictable onchain liquidity against LINK. Support for additional tokens is planned to be incorporated over time, such as additional blockchain-native gas tokens and stablecoins.