1. Is the niche too broad?
I would focus mainly on health benefits of plant-based foods, nutritional aspects of eating a plant-based diet, and, possibly, recipes.
2. Is it a buying market?
I understand that the best products, blogs, and website solve a specific problem that people need an urgent answer to. From that perspective, this doesn't fit the bill. I can set up a shop with products like plant-based recipe books, supplements, t-shirts etc. but it bothers me that people who eat a plant-based diet may not need to buy anything. For examples, they can get recipes online.