Why do you need to handle DDR5? You can use DDR3 to play the vast majority of competitive video games. It's not hard to find an FPGA that can handle DDR3 or DDR4.
You also don't need to sniff the entirety of the traffic. You just need to introduce aliasing. That is much harder to do for DDR5 but you don't need it to be reliable or stable for a long time, because you won't be sniffing for very long. And you don't need to do 6000+MT/s either.
As far as I know there are very few systems that support Windows 11 with DDR3.
I think his point was more that if you drop the link rate on ddr5 to sniff then the performance penalty will be very bad. DDR5 starts at 3000
You also don't need to sniff the entirety of the traffic. You just need to introduce aliasing. That is much harder to do for DDR5 but you don't need it to be reliable or stable for a long time, because you won't be sniffing for very long. And you don't need to do 6000+MT/s either.