I've just gone vegan, or am trying to go vegan.
I think shopping is quite a change. Migros could position itself wonderfully by labeling an entire REgal as vegan and all soy products, special milk, oat cream, etc. could be found there.
I think it would fit perfectly into the Generation M strategy and I'd come back to Migros instead of running to the health food store.
Why don't you do a pilot in a few stores? I would be delighted!