I've emailed walther in germany a while back and suggested to the idea of a single stack p-99 to make it slimmer and if they could maki it more compact. They replied saying that they will consider it. Keep your fingers crossed!!!
I consider the P99 with its 4-inch barrel as a compact handgun, as in a Colt Commander or Glock-19. If there had been a 5-inch version it would be a full-size. The 3-inch Glock-26 and new XD are marketed as Sub-Compacts. I hope Walther will have a 3-inch Subcompact version which can still use the current "full-capacity" magazine... not a single stack one. I don't like to have different magazines for a "same line" of model. Just like in glock where the 33-rdr Glock 18 mag fits on the dimunitive Glock-26. The grip of the P99 is slim enough. It is its' slide width where the changes would have to be. Its possible to slim it down to 1-inch. Kahr may have a .9-inch slide, but its grip would still make it thick enough.