What I really want is a trade-in system that pays out closer to what I'd get selling my Macbook on Craigslist or something. I want to stay within Apple's ecosystem and upgrade regularly, but I'd end up having to shell out nearly full price every time to do so, so I don't upgrade and no money changes hands at all. If they weren't quite so greedy with it, they could easily extract hundreds from me per year.

It seems like this might be what you're looking for then, depending on how the prices shake out.

What's interesting is that it somewhat reduces the pressure on Apple to have compelling new devices, if a large chunk of customers are constantly returning leased devices and getting new ones.