We’ve already had an Android 4.1.2 Jelly Bean firmware leak for the Xperia S (LT26i) and now the same has occurred for the Xperia ion (LT28i). The Jelly Bean firmware version is build number 6.2.B.0.203 and was intended for production devices. However, xda-developer legend, DooMLoRD, has managed to port the firmware to consumer handsets.
It will only work on handsets with unlocked bootloaders due to the need to flash a new kernel. DooMLoRD is currently in the process of uploading the ROM for users, so keep an eye on this thread for further details.
Thanks Aaron and Long!