Apple presumably killed it because it's incompatible with how they do scaled resolutions, which IMO is a pretty good reason.
(It's incompatible because sub-pixel rendering requires control over individual sub-pixels by strategically changing the colors of specific physical pixels. With scaled resolutions, the OS is rendering to a virtual resolution with virtual pixels, and the resulting image gets scaled down such that the virtual pixels don't correspond 1:1 with physical pixels. So the OS has no way to control sub-pixel brightness. If it tried to do sub-pixel rendering at the virtual resolution, by strategically adding colored fringes to text, the result would look like a multi-colored disaster when displayed on the physical monitor.)
The only time the lack of sub-pixel rendering would really matter is if you're running non-HiDPI on a low-resolution monitor... is that what you're doing, or intend to do?