In terms of plant-based alternatives, I think nutrition research could be high-impact and neglected. It seems like people are focused on trying to replicate the taste of meat, but when I experimented with veganism, I found myself wanting meat more the longer I’d gone without it, and experiencing it to be unusually satisfying if I hadn’t had it in a long while, which seems more compatible with a nutritional issue—the same pattern doesn’t seem to manifest for other foods I find tasty.
I’m imagining a study which feeds participants a vegan diet along with some randomly chosen nutritional supplements to see which are correlated with reduced desire to eat meat or something like that. Or maybe just better publicizing already known nutrition research / integrating it into plant based meat substitutes—for example, I just found this article which says iron from red meat is absorbed much more easily—I do think I was craving red meat specifically relative to other animal products. (Come to think of it, I was also experiencing more fatigue than normal, which seems compatible with mild anemia?)