Amazon’s quest to makes its Prime offering as sticky as possible continues, as it acquires PillPack, an online firm looking to outmaneuver pharmacists at a lower cost. But what’s the limit to Amazon’s expansion? Could it get as far as offering a Prime Life option, bundling everything one needs to live, before an antitrust regulator steps in? Is there a market for such a thing as Life-as-a-Service? PillPack’s schtick is that it can offer the service of a drugstore with the convenience of something like Amazon Prime. It’s a good fit for Amazon, but it also marks a threshold for the company – which has expanded into digital media and music, before heading into groceries with its monstrous Whole Foods…