I'm A Banana
Potassium-Rich
I have to admit that I forgot what they did to the Tiefling race which created the necessity of creating the "Planetouched Tiefling" as a word. It's the reason I don't like the appropriation of terms to mean something different from the intention of the original meaning.
For you and others who might not know:
4e tieflings are former humans who lived in the city of Bael Turath. There, they made a pact with Asmodeus, and gained great (and ambiguous) magical power (and also apparently devil horns the size of handlebars and a tail that makes stools a necessity if the 4e visuals are anything to go on) until their evil magical empire was brought low by the noble knightly Dragonborn and who now cling on in small enclaves and dark ruins and might be PC's for...whatever reason. Very sword & sorcery, pulpy, evil-magic-devil-pact kind of stuff. You can play an evil devil wizard, all proud and imperious and reminscent of decadence and the sins of ambition.
Planescape tieflings are humans born with some lower-planar "taint" on them. Perhaps there was a demon somewhere in their ancestry or a yugoloth performed experiments on their granddad or they just come from a city that was a little too close to the lands of evil, and they are born mutant and wrong, with horns and scales and tails and cloven feet and other deformities. This mark stigmatizes them, rendering them outsiders in society, castoffs who are assumed to be wicked and nasty simply for how they were born (and some of them, either due to nature or nurture, totally do turn out to be wicked and nasty). This is gray, urban fantasy where you explore the question of nature vs. nurture and the abuse society heaps on the marginal (the ill, the disabled, the deformed). You can play an outcast who rises above the society that casts them out to prove that it is not what you are born as but the choices you make that define you.
These are different aesthetics. A little superficially similar (humans tainted by evil), but very different core narratives. (Forex, there is no one to blame in the PS tiefling's story -- evil is a reality of the world that character lives in. For the Turathi tiefling, there is a specific historical sin that casts a stain that they are supposedly working to overcome.)
FWIW, dragonborn are also different in 4e, but are probably better in 4e than in their first incarnation. Gnomes are also different in 4e, and their story there is....meh (it's the "Escaped From Slavery By Evil Guys" story, again). But their story pre-4e is also a little meh (Okay, they're magical tricksters who love gems?).
So for me, while I hope they enable PS tieflings, I hope they also keep 4e dragonborn (even alongside 3e dragonborn, if anyone ever really cared about 3e dragonborn...), and hope they do something a little fresh with the gnome (but I should be able to recognize both gnomes in whatever they do). The gnome will be where I'm looking to be surprised.