From what I can tell of the block diagram, dropping the 2x 1gbit ports would not yield you a 2nd 10G SFP, as those would be running off the integrated switch as opposed to one of two USXGMII interfaces.
You would have to drop the other ports instead, and then you would just have 2x 10G SFP and a gigabit switch. Which is exactly how the BPi R4 is configured.
You would have to drop the other ports instead, and then you would just have 2x 10G SFP and a gigabit switch. Which is exactly how the BPi R4 is configured.