technically speaking (not that I am an expert
) a transaction with RBF flag is just another transaction in the mempool that miners can pick up and include in the blocks and there is nothing dictating they should not include this one or the next one based on the sequence in it.
Nodes will drop the one with the lower fee out of the mempool and the one with the higher fee will be in the mempool. If you send a transaction that can replace the previous transaction, most miners and nodes will drop the other transaction and include newer one.
besides as you said not many nodes or even miners have implemented this.
double besides as I have said your transaction would be an special one because you can contact those two guys and tell them someone is trying to scam you by double spending and take your payment.
I was talking about CPFP. Nodes who have upgraded would have opt in RBF enabled.
Timing. How sure are you that the previous transaction will not be included in a block before the replacement transaction gets included by other miners?
Besides, they don't have to help you.