The engadget article you linked to is over a year old. If that's what ypu mean by "SDIO driver" then it isn't what you think. He took the driver from the Tungsten T5, with a similar hardware design to the Treo, and hacked the drivers to override some checks that made sure it was actually running on a T5. After those checks were removed, the driver functioned on the Treo, albiet unstably.
It was a cool hack, but not even close to a Linux SDIO driver.