I think of Blue Apron, who ships fresh food and a fancy recipe so you can cook a gourmet meal at home. With WFM in the fold, Amazon could easily replicate that, with or without a subscription. Just create a bunch of awesome meals and let people choose one and ship the ingredients.
The other thing about Amazon is they tend to develop products for internal use (and perfection), and then roll them out as services. They can easily do this with a pharmacy and I predict they will do it with a payroll system.
Idle ramblings.