> Although it certainly isn’t a consensus opinion there is a real possibility that (given that the nervous system specialises what normal tissues can also do) plants are considerably more “conscious” than we give them credit for.

Yes, that is a possibility, but it's also an entirely ridiculous argument to make to argue against veganism. If you want to argue that the nervous system is just a more specialized version of other tissue and consciousness could therefore, in principal, arise in any kind of organic matter, or inorganic matter even, then one obviously can't prove that statement wrong, but it also seems to entirely miss the point given our current scientific understanding. Obviously humans cannot live in a way that completely avoids any (theoretical) harm to our environment, but veganism is by far the dietary choice that minimizes suffering in this world (though there do exist differences in the kind of vegan diet with regards to its environmental impact).