I'm disappointed, sure, but not despondent.
It's totally possible they're just trying to lock down what the "core" tiefling looks like for branding purposes, but will release possible subraces and alterations with upcoming splat and campaign guides.
Same way a Dark Sun book would presumably have sections detailing what makes a cannibalistic DS halfling from a core Lightfoot, bald dwarves, etc, they could be saving the "Planescape" tiefling for a later book with extra fluff and subraces.
It's totally possible they're just trying to lock down what the "core" tiefling looks like for branding purposes, but will release possible subraces and alterations with upcoming splat and campaign guides.
Same way a Dark Sun book would presumably have sections detailing what makes a cannibalistic DS halfling from a core Lightfoot, bald dwarves, etc, they could be saving the "Planescape" tiefling for a later book with extra fluff and subraces.