A week may seem like a short period of time to take a stock kit kat ROM and port it over to a phone that is virtually the same, but that is exactly what XDA Developer DoomLord did with the Google Play Edition Xperia Z Ultra and the Xperia Z1. The GPE Z Ultra released just last week alongside the LG Gpad 8.3, and while the news of the Gpad is an entirely different story for another day, the Z Ultra(running basically the same internals as the Z1) is running Kit Kat 4.4.2, so naturally, it makes sense that someone would want to help out the community of Z1 owners and gift them something that will last far through the holidays.
DoomLord says that the ROM is only partially working at the moment as there are some bugs in it, of which, a broken camera and broken WiFi features are present. There are a few more bugs than just those two, and this could definitely be a deal breaker for many, but those two broken features seems to be worst ones and if you happen to be someone who is on an Xperia Z1 and doesn't really use those two features much, you might want to head over to the XDA Thread that DoomLord has created regarding this ROM and give it a try.There are definitely still some improvements to be made before this should really be considered your daily driver, but its not too bad in its current state and expect DoomLord to be working hard to update it with fixes and get it running full steam without most issues. Go ahead. Don't feel bad or impatient for wanting to scrap whatever you have going on with your device at this very moment to load up this ROM. We know the temptation of Kit Kat is enough to make you want to put in the work to flash this, broken or not, and that's ok. We'd do it too. That being said, if you choose to move forward with flashing over this ROM, keep in mind the issues listed above along with the rest of the bugs that are currently present in this ROM which you'll find at the XDA thread. Lastly, you'll need an unlocked bootloader and your phone will have to be ROOTED to flash the ROM. A full list of flashing instructions will be available on XDA and you can check out some of DoomLords other works on his XDA profile. Happy holidays and have fun flashing!