Vortex have 2 series' of doubleshot "PBT" keycaps available, so it's not impossible to do, but I suspect they are using a PBT / ABS blend to get around the thermal expansion / contraction issues PBT has when molded.
I'm waiting for Ivan's GB. Genuine GMK Cherry profile doubleshot Dolch goodnes... Yum. ABS is quite acceptable if it's thick and Cherry profile.
This is a new GB or it is that black set that is already running?
A new GB that Ivan will start soon:
http://geekhack.org/index.php?topic=57303.msg1300820#msg1300820About PBT vs ABS, etc:
First off, I own and use the following sets: Keycool medium thickness PBT, Keycool medium thickness POM, SP DCS ABS (a few sets), stock Ducky thin ABS, stock KBT thin ABS. I'm waiting for some thick PBT dyesub sets to arrive. Will be ordering the Dolch thick ABS set when Ivan starts the GB.
PBT is denser than ABS and POM is denser than PBT. The weight of the keycap really does change the feel, as does the surface texture AND material. I like heavy keycaps. For keycaps of the same thickness, I prefer the densest material available. In terms of surface texture and feel I prefer the "slickness" of POM to the "dryness" of PBT. ABS is somewhere in between in terms of material feel. So for me it goes:
Thick POM>Thick PBT>Thick ABS>Medium POM>Medium PBT>Thin PBT>Thin ABS
Doubleshot>Dyesub>Lasered>Pad printed.
Because DS and Dyesub don't raise the legends, DS is clearer and lasts forever, and lasered lasts longer than printed.
If YOU can't feel a difference, it doesn't mean nobody can.