I''m running an OG 1996 Japanese P2 and a 2017 English P1. I'll be aiming for mimitchi and mametchi, but the chances of that happening are slimmer than Bandai America ever releasing a real Fantasy ON in English.
A difference I've noticed already is that the newer version sounds much higher pitched, and the buttons are much more responsive. Setting the clock on the new P2 is much faster as well.
Included the last picture because tamagotchi mitosis looks kinda cool.