It’s the blood elf model, not forsaken. That’s what I mean and you know it. I don’t think forsaken players want their customizations to include blood elf undead as options. Who would ever choose the original then? It’s too different.
My wish is after this patch, there be a small quest where the undead elves return to the Blood Elven fold now that Sylvanas isn’t in the picture, and voila the customization is unlocked. It might take a bit more lore tweaking than that but it’s feasible. Or they could just switch it on like they did with void elf fair skin and hair. Whatever.