The Gini Coefficient is not a significant indicator of the viability of an asset as collateral. We should be more concerned with its utility and security. An asset being held today by mostly one person or a small cohort does not mean it is risky. For example, Uniswap liquidity tokens can be created at any time from their backing assets, so it is not a big deal that two accounts hold 82% of Compound DAI Uniswap Liquidity. Also, different accounts are not necessarily different people or organizations.
By putting weight on the Gini Coefficient, we might be incentivizing would-be collateral tokens to airdrop their tokens, or temporarily spread them out by other means.