создай тему на редите, там девы ошиваются

First of all, nodes aren't required to keep full transactions (TxID will be enough). Also we don't need to keep them forever. I propose that nodes can forget about transactions received over an hour ago. Miners should be careful to include these transactions in block.

It's not a problem. Miners could keep and rebroadcast these transactions shortly before including them into the block.
The chain becomes valid anyway, when it receives two or three valid blocks. Also we can simply bypass this rule for some time after the launch. Also we can add a new type of message for the purpose of mempool synchronization between the nodes.

I propose to reject all transactions that conflicting any other transaction in node's mempool. But we have to keep original transaction and reset time when it was received. So it cannot be included into the block another 15 seconds. In addition we need to keep the transaction's size and update it every time when we are rejecting a conflicting transaction that larger then all previous such transactions.

For example. If node receives a transaction "A" which size is 400 bytes, it should keep this transaction and two additional values: { tx_A, 400, time }. If then after 10 seconds it receives a conflicting transaction "B" which size is 500 bytes, it should update these values as follows: { tx_A, 500, time+10 }. If it receives another conflicting transaction "C" after another 5 seconds which size is 550 bytes, it should update the values: { tx_A, 550, time+15 }.

When node is validating the block and found some transaction that conflicts with a transaction in it's mempool, it should check that size of this transaction is not more then stored size. If it is so, the transaction shouldn't be considered as spam. Thus miners cannot include their own transactions into the block for free and cannot spam nodes' mempools with conflicting transactions.