Mind you that a tx in the mempool has not yet produced any changes to state. In BTC you can also replace-by-fee for instance (https://en.bitcoin.it/wiki/Transac

Mind you that a tx in the mempool has not yet produced any changes to state. In BTC you can also replace-by-fee for instance (https://en.bitcoin.it/wiki/Transaction_replacement https://en.bitcoin.it/wiki/Transaction_replacement). This page (https://github.com/ethereum/wiki/wiki/Design-Rationale https://github.com/ethereum/wiki/wiki/Design-Rationale) contains a good overview of the UTXO vs Account model with each's strengths and weaknesses.