Disagree. There was enough controversy over Bitcoin Cash such that we knew it would not have majority out of the chute*. But S2X has -- or at least had -- overwhelming support. If you think the change is likely to capture the majority by the outset, you do not implement replay protection. You let the to-be-minority implementation act to protect itself best it can. Best case, the legacy implementation dies near-immediately. Has core implemented replay protection for any of their changes?

*over the coming months is another story altogether.