I might have missed something, can anyone confirm?
Given that the Due is 3v3 and standard Arduinos are mostly 5v, for which most shields are primarily designed, this is probably the most important compatibility issue.
Not so, if you wish to use UDP to handle 400KB/s then it falls over, but low volume traffic is ok, persuading it to work with other SPI devices (Flash IC, SD Card) can be great fun!! Ping, NTP, UDP all at the same time? Good luck with that.
3.3V is seen as a logic high by 5V devices so yes, you can stick it on the DUE, the other way round however and things tend to go pop or fizz or bang.........
Are these Due/Eth2 specific compatibility issues or general problems?