B12 is one of the least problems, because there are several kinds of bacterial cultures that produce it with high efficiency.

The research for improving the production of other kinds of vitamins is more active, by trying to either discover or create bacterial strains suitable for this purpose.

A serious problem is that unlike the production of traditional food, the production of vitamins and nutritional supplements is concentrated in a few countries, and mostly in China.

So if overnight everybody would become vegan, then suddenly most of the world would become nutritionally dependent on China.

Ideally every bigger city should be able to produce the vitamins needed by its inhabitants, like it is able to produce other staple foods, but we are very far from this when entire countries may not have any vitamin production facility.

And taurine