Thanks @Agusx1211! One potential issue with this is that during the transition period during which both legacy and EIP1559 transactions are accepted the MAX_GAS_EIP1559 is split between the two gas pools. For example, at the block that EIP1559 is activated 8m is in the legacy pool and 8m is in the 1559 pool. So a transaction to either pool with gas usage of MAX_GAS_EIP1559 would be rejected. This would be the case until the EIP finalization block is reached and the entire MAX_GAS_EIP1559 is available to the 1559 pool.
Perhaps the TX_GASLIMIT could be set to the portion of MAX_GAS_EIP1559 available for processing that type of transaction at a given blockheight. But that will still cause issue for smart contracts that assume they can use the whole block for gas.
We’ve raised the TARGET_GAS_USED to 10m since that is the current gas limit, but I am hesitant to raise MAX_GAS_EIP1559 to 20m. It was originally set to be 24m, but there were some concerns raised by Péter and in our Core Dev’s call about the ramifications of this (EIP-1559: Fee market change for ETH 1.0 chain).