DeFi is a very innovative field indeed. What I find most appealing is that some popular derivative protocols are yet inefficient in some ways, which means there is a lot of room for new solutions to come along.

For instance, I'm interested in options trading, and there is a lot of competing protocols [1] each one with it's advantages and disadvantages. One of the most popular, Hegic [2], employs liquidity pools pricing options at a really expensive value due to a simplified pricing model (good for writers).

Shameless plug: I myself have been playing with smart contracts in my free time and deployed a tokenizable options trading decentralized exchange [3] (on kovan testnet nonetheless!) trying to address some os these points. Learned a lot implmementing it, and I find amazing that anyone can come up with their own DeFi solution.

[1] https://medium.com/coinmonks/an-update-of-a-comparison-of-de...

[2] https://www.hegic.co/

[3] https://github.com/TCGV/DeFiOptions