The idea of using cardano for bitcoin defi could be promising especially with its focus on security and UTXO based transactions. However, as you mentioned there's a growing number of layer 2 networks that aim to address bitcoin's scalability issues. For Cardano to carve out a niche in this crowded space it would need to bring unique advantages, whether through better transaction speed, lower costs or enhanced security features. I'd need to see more detailed plans before deciding if it's worth pursuing for bitcoin defi.