Also find the recent CVE related to RBF by Antoine Riard and implementation of RBF in Bitcoin Core compared to btcd interesting. Even though I am not sure why inherited signalling is not implemented in Bitcoin Core.

RBF, CPFP and their combinations are something that is less explored IMO. For example: I had discussed one usecase of CPFP with Harding in IRC once in which a project uses maker-taker model. Maker broadcasts transaction with 1 sat/vByte and taker has to confirm this transaction by creating a child transaction with an effective fee rate according to mempool stats. Basically, the idea of receiver paying for the transaction instead of sender. But it will involve lot of exception handling.