Hey Riley! Welcome to the forum–looks like we’re both making our first posts. 
The UNI token has a higher market cap than some tokens already being used as collateral on both Arbitrum and Optimism v3. If you’re interested in getting the ball rolling, it’s worth submitting an Aave Request for Comments (ARC) that includes some relevant risk data and a justification for allowing UNI to be used as collateral.
You can learn more about the process of proposals and their implementation in this forum topic and the governance docs.