Regarding the Alhambra line, I think VCA is stuck between a rock and a hard place. (Pun intended) I think there are very few stones that can work in and Alhambra setting and shape because the setting is so thin/narrow width wise. Amethyst, citrine, moonstone and other more transparent gemstones will look
dead when cut to the Alhambra specifications. Other, more translucent gemsones are difficult to source in the quality and quantity required, or are too soft to work. That's why porcelain has been offered.
I think pink opal or rose quartz could be really pretty. Or even some Vietnamese or other highly included ruby/sapphire material because the inclusions can be stunning, much like malachite/tiger's eye striations. I own a ruby bangle (all one stone cut like a jade bangle) from Vietnam and it is spectacular. Since corundum is so hard, it would probably be difficult to work with and therefore would make the pieces $$$$.
Another pretty solution is to alternate pave motifs with pink/yellow/blue/purple sapphires or tsavorites. Since they work with these stones regularly in other settings.