Vitamin-A enriched foods are indeed a solution that can be implemented by swapping a single component of an ecosystem rather than the complete overhaul that you're proposing.
Sure, I mean - let's just simplify the whole system. 1 Cup of genetically infused full daily-meal Rice®™℠ for every single person on the planet. One cup sized serving portion of nutrient material. Yum.
"Yum" is not the point though, it's avoiding malnutrition, starvation and death. Maslow's hierarchy of needs and all that, survive first, then later when they're not dead they can worry about producing culinary delights.