> under the categorical ethics usually applied to argue for veganism, recognizing plants as sentient would make eating either inexcusable

Veganism is the ethical position that animals should not be exploited for food, clothing and other purposes. If you want to start a Compassion for Carrots organization, be my guest, but please don't form conjecture on others' behalf. You've also not yet provided evidence for plants' sentience, so you haven't actually given reason for considering the abuse of animals to be ethical or acceptable.