Sure, but once the text is cached in a layer that layer might be rotated or scaled or similar, in which case subpixel antialiased text would cause ugly artifacts. Keeping subpixel antialiased text in the layer and re-rendering the layer without subpixel antialiasing when a rotating or scaling animation starts would lead to stutters in the animation.

Looking forward to high DPI displays obsoleting subpixel antialiasing as it leads to a bunch of problems when wanting to create fluidly animating UIs.