When the moment comes it's pretty likely that Apple release it, even capped would trash the x86 laptops of that price, forcing Intel and AMD to be more agressive.
Apple doesn't really see the PC market as competition, so why should they bother? Like I've said many times, buyers make the "Mac vs PC" decision FIRST, then decide what to buy. There just aren't a lot of people who are open to either one who are in the "I would get a Mac if they were cheaper" camp. Its a lot easier to switch between iPhone and Android and while there is movement there aren't that many people who will switch between them multiple times. Most of the switchers are doing so for a reason, and are unlikely to ever switch back.
Apple offering cheaper iPhones makes sense in a way that offering cheaper Macs doesn't. Apple wants to expand the installed base of iPhones, because they get post sale revenue via the App Store. They don't benefit in the same way from having a larger installed base of Macs. Sure, they want more Mac owners, but they aren't willing to sacrifice margins to get them.
Apple wants to take the high end of the PC market, where the profit is. They don't care about the lower end, there's no money there and all having a cheap Mac would do is steal sales from the current "low end", Macbook Air.