Ah, I see now what you mean by "euphemism treadmill", and I agree that the framework is valid.

If the term has a chance of avoiding the treadmill I suspect it'd be due to the awkwardness of identifying as such. "Vegan" can apply to both food and the people who consume just that food, but I don't see people calling themselves "plant-based" anytime soon. The tribal aspect of the context is potentially greatly diminished by removing that explicit identity.