Many examples already exist, some less dramatic than others.

1. A one-person corporation where the individual's personal brand/skills are the main asset is effectively a publicly traded person if he/she accepts investors. The limited liability feature protects the person and prevents the model from turning into (well somebody had to say it out loud), slavery.
2. A paycheck is basically a 2000-hour/year time option. That's about 23% of your available time, so that's effectively 23% ownership. Your employer has the option, but not the obligation, to use that time effectively, and buys you up in a pay-as-you go model, one hour (retail) or 2-4 weeks (wholesale) at a time. In traditional employment, if the employer does NOT exercise the option, you have to sit around and wait. Hence the idea of "time theft." (the fact that you have to steal your own time back means it is not yours). That's why you need to sneak around playing Minesweeper, and keep Excel open on a suitably important looking spreadsheet, ready to maximize in case your boss walks by. Your time is also tradeable internally by the employer (hence the idea of "loaning" people across departments, which is really selling time-shares)
3. Slicing differently, a paycheck means the employer owns all your original ideas, but has no legal authority over (say) your bathroom habits. You could consider that securitization of a chopped-up human. Legally, The Man owns 100% of your creative brain, but less of your other body parts (the default being 23% for parts that come along for the ride by virtue of being attached to the parts that are used). This means cubicle-farm workers are more owned (pwned?) than remote workers, because the latter only rent out their brain, not the rest of the body. Hence the pajama commute.

An interesting question is: what do more explicit forms of person-ownership/trading do in real terms, ignoring any PR/marketing fanfare about it. The existing mechanisms seem to have pretty comprehensively allowed for very flexible ownership models.

Addendum, based on an interesting email sidebar with a friend. The real question is not whether you can buy and trade people (you can and have always been able to in history), but how LIQUID the marketplace for people is.

Paychecks represent a very illiquid marketplace. Consultants sell themselves in more liquid ways.