At this stage, it's very much a "True Scotsman" situation. But as I see it, companies are advertising for Full Stack Engineers as a way of getting people who would never say "Why did you give me this task?! This is outside my job description."

From what I see around me, while most everyone seems to say that this is a good thing, in practice almost everyone in such a position is seeking to move to either a management role or a specialist role, or just to launch their own business, at which point they're by definition an entrepreneur rather than an engineer.