Quite cool Aave v4 feature is risk premium: You pay higher borrowing rate if your collateral is riskier (on top of base rate). Safer collateral (wETH, USDC) = cheaper borrow. Riskier collateral = you pay more. In v3 all collateral had flat rate. Basically, if Curve founder wanted to lend CRV on Aave v4 to borrow stablecoins, he would pay much higher borrowing rate than if collateral was ETH(Ignas | DeFi)